Communication apparatus, relay apparatus, communication system and communication method

ABSTRACT

It is expected to provide a communication apparatus, relay apparatus, communication system and communication method for effectively performing a communication timing adjustment when a collision has occurred on a communication line, efficiently reducing the communication collision with reducing processing loads on each apparatus, for making each apparatus effectively perform the transmission timing adjustment, and for improving the communication efficiency. ECUs are connected to communication lines with a bus topology. A relay apparatus is connected to the communication lines, obtains a time distribution based on a number of messages transmitted to the communication lines. When the bias occurs in the transmission timings, the relay apparatus transmits an instruction message that instructs to perform the timing adjustment for messages transmitted between the ECUs. In addition, it is determined whether a message to be relayed is held. When it is determined that such a message is held, the instruction message is transmitted.

This application is the national phase under 35 U.S.C.§371 of PCTInternational Application No. PCT/JP2009/005835 which has anInternational filing date of Nov. 3, 2009 and designated the UnitedStates of America.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a communication system transmittingdata among plural apparatuses. Particularly, the present inventionrelates to: a communication apparatus that can reduce a communicationcollision on a communication line to which the apparatuses are connectedand that can improve communication efficiency a relay apparatus that canimprove communication efficiency for relaying to another communicationline; a communication system including the communication apparatus orrelay apparatus; and a communication method with the communicationapparatus or relay apparatus.

2. Description of Related Art

Recently, several fields utilize a system in which plural apparatusesare connected, a function is assigned to each apparatus, the pluralapparatuses mutually exchange data, and the communicating pluralapparatuses implement several operations. For example, a field ofon-vehicle local area network (on-vehicle LAN) mounted on a car utilizesa system in which a specialized function is assigned to each electroniccontrol unit (ECU), the plural ECUs are connected with a communicationline to mutually exchange data, and the communicating plural ECUsimplement several operations.

Much more specialized function have been assigned to the ECU, the ECUhas been able to implement much more various functions, and then, acommunication line has been connected to a larger number of ECUs andmuch more various types of ECUs. Such a system is further expected toimplement a larger variety of operations, and thus, a transmitted dataamount is expected to be larger because ECUs must share data andcommunicate to each other.

When the communication line transmits a larger amount of data, datacollision (conflict) may occur which causes a data delay. A significantdata delay may bring a fatal event to a driving function implemented byan ECU, such as a brake control.

FIG. 23A and FIG. 23B are explanation views showing an example casewhere the data collision occurs in data transmitted from ECUs on acommunication line. FIG. 23A shows a configuration where an ECU (A), ECU(B), ECU (C), ECU (D) and ECU (E) are connected with a bus topology. Inthis configuration, it is possible to transmit data when eachcommunication line is opened. FIG. 23B shows a time sequenceillustrating a data transmission timing of each ECU. As shown in FIG.23A and FIG. 23B, each ECU transmits data at a predetermined interval.The predetermined interval is almost fixed for each ECU, although thepredetermined interval may be changed a little due to the performance ofECU. Predetermined intervals of respective ECUs may be set differentlyfrom each other, e.g., 10 milliseconds, 12 milliseconds, 15milliseconds, in order to avoid the collision of transmitted data.However, there is a timing at which plural ECUs try to transmit dataalmost simultaneously as shown by the time point “t” in FIG. 23B, i.e.,a cycle that is the least common multiple of predetermined transmissionintervals for respective ECUs. This timing cyclically comes and causesthe data collision.

It is known that a definition; such as the FlexRay, controls datatransmission with a time triggered protocol (TTP). Such a definitiondivides a predetermined communication cycle of each ECU and allows thecommunication at an assigned period, in order to avoid the datacollision. However, it is preferred to be free from the constraint basedon the time triggered protocol definition, and to prepare a definitionapplicable to the controller area network (CAN) that is typicallyutilized for the on-vehicle LAN and performs an event triggered control.

A patent document 1 proposes a control technique that utilizes a methodapplicable to the CAN and prevents the data collision caused bycommunication interference between ECUs. In the technique disclosed bythe patent document 1, each ECU includes a time measuring means,measures a timing of data transmitted from another ECU, decides own datatransmission timing to start transmitting data after another ECUcompletes data transmission, in order to avoid the communicationcollision.

In addition, it is known to divide a communication line into severaldifferent communication lines, to connect each ECU to a differentcommunication line, to utilize a relay apparatus (gateway apparatus) forconnecting the different communication lines, and to make the relayapparatus relay data, in order to avoid the collision caused by theincreased number of ECUs connected to communication lines (e.g., patentdocument 2). Because these configurations reduce the number of ECUsconnected to communication lines, it may be possible to reduce acommunication amount and to avoid the data collision and the like. Inthese configurations, it may be further possible to save requiredcommunication lines and to avoid the collision, when ECUs sharing dataare classified into a same group.

A patent document 3 discloses a technique in which ECUs utilized in theon-vehicle LAN field are classified into plural groups, ECUs classifiedin each group are connected to one communication line, and onecommunication line is connected to another communication line by a relayapparatus (gateway apparatus), in order to preferably relay highpriority data based on the priority provided to transmitted message, andto prevent the transmission of high priority data from being delayedsignificantly even when the amount of communication loads are increasedon communication lines.

The “priority” corresponds to a message ID provided to a message in theCAN typically utilized for the on-vehicle LAN, and the CAN is defined topreferably transmit a message provided with a smaller number in the casethat the message ID is interpreted as such a number (non-patent document1).

When a relay apparatus tries to relay a message received from an. ECUconnected to one communication line toward another communication line orrelay a message created from the received message toward anothercommunication line, the relay apparatus may not enable relaying becauseof lower priority in the case that another communication line isutilized for transmitting high priority message greater than the messagetransmitted through said one communication line. At that time, there maybe another message to be relayed from said another communication linewhich is held without being transmitted.

Even if these messages should be simultaneously received by an apparatusrequiring these messages in this case, one of these messages is heldwithout being relayed by the relay apparatus. Therefore, it is notpossible to keep the simultaneous message reception. Hence, it isconsidered to utilize a method adjusting the transmission timing foreach message, in order to prevent the message from being held due to therelay apparatus. The method utilizes the invention disclosed by thepatent document 1. In the method, each ECU includes the time measuringmeans, measures the timing of data transmitted from another ECU, decidesown data transmission timing to start transmitting data after anotherECU completes data transmission, in order to avoid the communicationcollision.

-   [Patent Document 1] Japanese Patent Application Laid-Open No.    2007-60400-   [Patent Document 2] Japanese Patent Application Laid-Open No.    2002-16614-   [Patent Document 3] Japanese Patent Application Laid-Open No.    2005-159568-   [Non-Patent Document 1] CAN Nyuumonsho    (URL:http://documentation.renesas.com/jpn/products/mpumcu/apn/rjj05b0937_canap.pdf),    Jan. 31, 2006, Renesas Electronics Corporation, online searched on    Aug. 25, 2008.

SUMMARY OF THE INVENTION

The technique disclosed by the patent document 1 may avoid thecommunication collision between apparatuses connected with a bustopology. However, in the case of utilizing a configuration thatdetermines the transmission timing based on a data transmission from apredetermined apparatus, there is a risk that the transmission timingsfor all apparatuses other than the predetermined apparatus cannot bedetermined when a failure happens to the predetermined apparatus and thepredetermined apparatus cannot transmit data. In addition, in the caseof utilizing a configuration that independently makes each apparatusdecide the transmission timing based on a data transmission from anotherapparatus, respective decided transmission timing may not convergeefficiently.

Further, in the case of utilizing a configuration that independentlymakes each apparatus count the data transmission from another apparatusall the time to determine the transmission timing, each apparatus musttake a larger amount of processing load. When there is no transmissiondata on the communication line, it is not required to make eachapparatus determine the transmission timing.

The present invention is made in view of such circumstances, and has anobject to provide a communication apparatus, communication system andcommunication method, where plural apparatuses are connected to acommunication line with a bus topology, each apparatus performstransmission timing adjustment, a communication apparatus connected tothe communication line perform the transmission timing adjustmenteffectively at the time when a collision occurs on the communicationline, the communication collision is reduced efficiently as well as theprocessing load amount is reduced for each apparatus, and each apparatusperforms the transmission timing adjustment effectively, in order toimprove the communication efficiency.

The present invention has another object to provide a relay apparatus,communication system including the relay apparatus and communicationmethod utilizing the relay apparatus, where a relay apparatus isutilized for relaying message transmission between plural apparatusesconnected to a communication line with a bus topology, a message isprevented from being held by the relay apparatus, the communicationcollision is reduced efficiently as well as the processing load amountis reduced for each apparatus, and the communication efficiency forwhole communication system is improved.

A communication apparatus according to a first aspect of the presentinvention is connected to a communication line to which pluralapparatuses transmitting messages are connected with a bus topology,receives a part or all the messages transmitted to the communicationline, and comprises: a means for determining whether it is required forperforming a timing adjustment of a message transmission on thecommunication line or not; and a means for transmitting a messageinstructing to perform the timing adjustment of the messagetransmission, when it is determined by the means that it is required forperforming the timing adjustment of the message transmission on thecommunication line.

A communication apparatus according to a second aspect the of presentinvention is connected to a communication line to which pluralapparatuses transmitting messages are connected with a bus topology,receives a part or all the messages transmitted to the communicationline, and comprises: a counting means for counting a number of messagestransmitted during a predetermined monitoring period that is dividedinto plural time intervals; a determining means for determining inaccordance with a number of messages counted for each of the plural timeintervals by the counting means whether it is required for performing atiming adjustment of a message transmission between the pluralapparatuses or not; and a means for transmitting a message instructingto perform the timing adjustment of the message transmission, when it isdetermined by the determining means that it is required for performingthe timing adjustment of the message transmission between the pluralapparatuses.

A communication apparatus according to a third aspect of the presentinvention includes the determining means that comprises a means fordetermining whether a number of time intervals in which a message cannotbe transmitted is not less than a predetermined number among the pluraltime intervals, and that determines to perform the timing adjustment ofthe message transmission when it is determined that the number of timeintervals is not less than the predetermined number.

A communication apparatus according to a fourth aspect of the presentinvention includes the determining means that comprises a means fordetermining whether a number of messages in one or more time intervalsamong the plural intervals is not less than a predetermined number, andthat determines to perform the timing adjustment of the messagetransmission when it is determined that the number of messages is notless than the predetermined number.

A communication apparatus according to a fifth aspect of the presentinvention includes the determining means that comprises a means fordetermining whether the maximum in numbers of messages during the pluralintervals is not less than a predetermined-fold of the minimum in thenumbers of messages during the plural intervals, and that determines toperform the timing adjustment of the message transmission when it isdetermined that the maximum is not less than the minimum.

A communication apparatus according to sixth aspect of the presentinvention includes the counting means that utilizes the predeterminedmonitoring period as a cycle and periodically counts at each cycle, andfurther comprises: a means for determining that the determining meanssequentially determines not less than predetermined times that it is notrequired for a cycle; and a means for transmitting a message instructingto stop the transmission timing adjustment toward the communicationline.

A communication apparatus according to seventh aspect of the presentinvention further comprises a means for determining a time point when amessage instructing to perform the transmission timing adjustment istransmitted, in accordance with a distribution of messages counted bythe counting means in each time interval during the monitoring period,wherein the message instructing to perform the transmission timingadjustment is transmitted toward the communication line at thetransmission time point, when the determining means determines that itis required.

A relay apparatus according to eighth aspect of the present invention isconnected to plural communication lines to which plural apparatusestransmitting messages are respectively connected with a bus topology,includes a means for receiving a part of or all of messages transmittedfrom each apparatus connected to one of the communication lines and astoring means for storing a received message, relays a stored message toan apparatus connected to another of the communication lines, andcomprises: a determining means for determining whether a messagetransmitted from an apparatus connected to said one of communicationlines is held or not; and a transmitting means for transmitting aninstruction message instructing to perform a timing adjustment ofmessage transmission between the plural apparatuses toward said one ofcommunication lines, when the determining means determined that themessage is held.

A relay apparatus according to a ninth aspect of the present inventionincludes the determining means that comprises a means for clockingelapsed time since a message is received and determines that the messageis held, when the elapsed time is not less than a predetermined time.

A relay apparatus according to a tenth aspect of the present inventionincludes the determining means that comprises a means for counting anumber of messages stored by the storing means, wherein it is determinedthat the message is held when the number of messages is not less than apredetermined number.

A relay apparatus according to an eleventh aspect of the presentinvention includes messages are respectively transmitted cyclically,wherein the relay apparatus comprises a means for identifying atransmission cycle of the messages stored by the storing means, when thedetermining means determined that the message is held, and thetransmitting means transmits the instruction message at a timing basedon the identified transmission cycle.

A relay apparatus according to twelfth aspect of the present inventionincludes the transmitting means that continuously transmits theinstruction message until the determining means has determined that themessage is not held.

A communication system according to a thirteenth aspect of the presentinvention includes plural apparatuses transmitting messages and a relayapparatus which is connected to plural communication lines to which theplural apparatuses are respectively connected with a bus topology, thatreceives a part of or all of messages transmitted from each apparatusconnected to one of the communication lines and that relays to anapparatus connected to another of the communication lines, wherein therelay apparatus comprises: a means for counting a number of messagestransmitted to one of the communication lines during a predeterminedmonitoring period divided into plural time intervals; a determiningmeans for determining in accordance with the number of messages countedduring the plural time intervals whether it is required to perform atiming adjustment of transmission between plural apparatuses connectedto said one of communication lines or not; and a means for transmittingan instruction message instructing to perform the timing adjustment oftransmission between the plural apparatuses toward said one ofcommunication lines, when the determining means determined that it isrequired, and each of the plural apparatuses comprises: a means fordetecting a time point when a specified message is transmitted, when theinstruction message is received; and a means for adjusting, inaccordance with a time lag between the detected time point and a timepoint when a message is transmitted by said each of the pluralapparatuses itself, a next time point when a next message is transmittedby said each of the plural apparatus itself to shorten the time lag.

A communication system according to a fourteenth aspect of the presentinvention includes plural apparatuses cyclically transmitting messagesand a relay apparatus that is connected to plural communication lines towhich the plural apparatuses are respectively connected with a bustopology, that includes a means for receiving a part of or all ofmessages transmitted from each apparatus connected to one of thecommunication lines and includes a means for storing received messages,and that relays to an apparatus connected to another of thecommunication lines, wherein the relay apparatus comprises: a holddetermining means for determining whether a message transmitted from anapparatus connected to said one of communication lines is held or not;and a transmitting means for transmitting an instruction messageinstructing to perform a timing adjustment of message transmissionbetween the plural apparatuses toward said one of communication lines,when the hold determining means determined that the message is held, andeach of the plural apparatuses comprises an adjusting means foradjusting a message transmission timing in association with anotherapparatus.

A communication system according to a fifteenth aspect of the presentinvention includes the relay apparatus that comprises a means fortransmitting a message identification information at the time when thetransmitting means transmits the instruction message, wherein themessage identification information is for identifying a message storedby the storing means, the transmitting means comprises a means foridentifying a transmission cycle of the message and transmits theinstruction message at a timing based on the identified transmissioncycle, and the adjusting means of each of the plural apparatusescomprises: an identifying means for identifying a timing when theinstruction message is transmitted; a determining means for determiningwhether a message identified by the message identification informationtransmitted together with the instruction message is transmitted by saideach of the plural apparatus itself or not; and a means for making atransmission timing of the message become close to the timing identifiedby the identifying means, when the determining means determined that themessage is transmitted by said each of the plural apparatus itself.

A communication system according to a sixteenth aspect of the presentinvention includes the plural apparatuses, each of which comprises ameans for making the transmission timing of the message become far fromthe timing identified by the identifying means, when the determiningmeans determined that the message is not transmitted by said each of theplural apparatus itself.

A communication method according to seventeenth aspect of the presentinvention is for communicating between plural apparatuses transmittingmessages and a communication apparatus that is connected to acommunication line to which the plural apparatuses are respectivelyconnected with a bus topology and that receives a part of or all ofmessages transmitted to the communication line, wherein thecommunication apparatus counts a number of messages transmitted during apredetermined monitoring time interval divided into plural timeintervals, the communication apparatus determines in accordance with thecounted number of messages at each of the plural time intervals whetherit is required to perform a timing adjustment of transmission betweenthe plural apparatuses, and the communication apparatus transmits amessage instructing to perform the transmission timing adjustment whenit is determined that it is required to perform the timing adjustment.

A communication method according to an eighteenth aspect of the presentinvention is for communicating between plural apparatuses transmittingmessages and a relay apparatus that is connected to a communication lineto which the plural apparatuses are respectively connected with a bustopology, that includes a means for receiving a part of or all ofmessages transmitted from the communication line and a storing means forstoring received messages, and that relays a stored message to anapparatus connected to another communication line, wherein the relayapparatus determines whether a message transmitted from an apparatusconnected to one communication line is held or not, the relay apparatustransmits an instruction message instructing to perform a timingadjustment of transmission between the plural apparatuses toward saidone communication line, when having determined that the message is held,and the plural apparatuses respectively adjust a message transmissiontiming in association with another apparatus when having received theinstruction message. According to the first aspect, messages arerespectively transmitted from the plural apparatuses connected to thecommunication line with the bus topology toward the communicationapparatus (relay apparatus) that determines whether a message adjustmentshould be performed for the communication line or not. When it has beendetermined that the message adjustment should be performed, thecommunication apparatus (or relay apparatus) transmits a messageinstructing to perform a transmission timing adjustment to eachcommunication apparatus. Thus, each apparatus performs the transmissiontiming adjustment only on a timing that is considered to need taking theadjustment. The plural apparatuses are connected to the communicationline, and may try to perform the transmission timing adjustment inassociation with each other in response to the message transmitted fromthe communication apparatus to the communication line, which instructsto perform the transmission timing adjustment. Therefore, it is notrequired to constantly perform the transmission timing adjustment, andit is possible to reduce the load on each apparatus.

According to the second, thirteenth and seventeenth aspects, thecommunication apparatus or the relay apparatus among the pluralapparatuses counts the number of messages on the communication lineduring the predetermined monitoring time interval divided into pluraltime intervals, and determines in accordance with plural numbers, eachof which is counted for messages at each time interval, whether it isrequired to perform the transmission timing adjustment for eachapparatus.

According to the third aspect, it is determined that the transmissiontiming adjustment is required, when a number of time intervals whosecounted messages are zero are not less than a predetermined number amongthe plural time intervals included in the monitoring period. In the casethat there is a time interval whose number of transmitted messages iszero, it is surmised that the bias may occur on the message transmissiontiming. It is enough to perform the transmission timing adjustment atthe case that such a bias is surmised. Therefore, it is not required toperform the constant adjustment.

According to the fourth aspect, it is determined that the transmissiontiming adjustment is required, when there is a time interval whosecounted number of messages is not less than a predetermined number amongthe plural time intervals included in the monitoring period. In the casethat there is a time interval whose number of transmitted messages isnot less than a predetermined number, it is surmised that the bias mayoccur on the message transmission timing. It is enough to perform thetransmission timing adjustment at the case that such a bias is surmised.Therefore, it is not required to perform the constant adjustment.

According to the fifth aspect, it is determined that the transmissiontiming adjustment is required when a number of messages transmittedduring a time interval in which the maximum number of messages aretransmitted during the plural time intervals included in the monitoringtime interval (i.e., maximum number) is not less than apredetermined-fold of number of messages transmitted during a timeinterval in which the minimum number of messages are transmitted duringthe plural time intervals included in the monitoring time interval(i.e., minimum number). In the case that there is a time interval whosenumber of transmitted messages is not less than a predetermined-fold ofthe number of another time interval, it is surmised that the bias mayoccur on the message transmission timing. It is enough to perform thetransmission timing adjustment at the case that such a bias is surmised.Therefore, it is not required to perform the constant adjustment.

According to the sixth aspect, the monitoring period is utilized as areference of one cycle and messages are counted cyclically. It isinstructed to stop the transmission timing adjustment, when thetransmission timing adjustment is determined to be not required forsequential cycles not less than predetermined cycles in accordance withthe counted number of messages during plural time interval in eachmonitoring period. In the case that the number of messages transmittedis uniformed for the monitoring period to some degree that thetransmission timing adjustment is not required, each apparatus is notrequired to perform the transmission timing adjustment in associationwith another apparatus.

According to the seventh aspect, a timing is determined in accordancewith the distribution of message number at each time interval in themonitoring period, and thus a message instructing to perform thetransmission timing adjustment is transmitted at the determined timing.For example, in the case that a time interval having a smaller number oftransmitted messages or, to the contrary, having a larger number oftransmitted messages is identified in time intervals included in themonitoring period and thus it is determined that the transmission timingadjustment should be performed, the message instructing to perform thetransmission timing adjustment is transmitted at a corresponding timeinterval in the next monitoring period. It is possible to startperforming the transmission timing adjustment at the time point wheneach apparatus has received the message instructing to perform theadjustment. Therefore, the transmission timing can be adjustedefficiently in the case that the message instructing to perform theadjustment is adequately transmitted at the effective timing.

According to the eighth, fourteenth and eighteenth aspects, a message istransmitted from an apparatus connected to a predetermined communicationline, and the transmitted message is temporarily stored by storingmeans. The relay apparatus relaying to another communication linedetermines whether a message is held without being transmitted from thecommunication line to another communication line. When the message isheld, the relay apparatus transmits the instruction message instructingto perform the transmission timing adjustment for the apparatusesconnected to the predetermined communication line. Thus, it is possibleto adjust the transmission timing of the held message and thetransmission timing of another message transmitted at around the sametiming. Therefore, it is expected to prevent the message from being heldlonger and greater at the relay apparatus after the adjustment. Inaddition, it is not required for each apparatus to perform thetransmission timing adjustment constantly, but it is enough for eachapparatus to perform the transmission timing adjustment at the requiredtime, in order to avoid the transmission collision on the communicationline. Therefore, it is efficient and the processing load is also reducedfrom each apparatus.

According to the ninth aspect, the determination whether a message isheld or not is performed in accordance with the elapsed time since themessage is received by the relay apparatus. When the elapsed time is notshorter than a predetermined time, it is surmised that the delay occursin the relaying processing. The adjustment should be performed in orderto prevent another message from being further transmitted and to preventmessages from being held longer and greater.

According to the tenth aspect, the determination whether a message isheld or not is performed in accordance with the number of messages thatare received by the relay apparatus and stored by the storing meanswithout being relayed. When the number of messages is not smaller than apredetermined number, the adjustment should be performed in order toprevent another message from being further transmitted and to preventmessages from being held longer and greater.

According to the eleventh aspect, each message is transmittedcyclically. In the case that a message is held without being relayed bythe relay apparatus, an instruction message is transmitted at a timingcorresponding to the transmission cycle of the held message, in order toinform the transmission cycle of the held message to an apparatustransmitting another message. Each apparatus can receive the instructionmessage, and can recognize that the cycle of received instructionmessage is equal to a transmission cycle of message that is not easilytransmitted to another communication line. Therefore, it is possible tomake own transmission timing become different from the transmissioncycle.

According to the twelfth aspect, the instruction message is sequentiallytransmitted during the time interval determined that the message holdoccurs. Each apparatus performs the transmission timing adjustment formessages, in accordance with the instruction message. When it has beendetermined that the message hold is solved, the transmission ofinstruction message is stopped and the transmission timing adjustment isstopped. Therefore, it is possible to perform the transmission timingadjustment only at the required time.

According to the fifteenth aspect, an instruction message is transmittedat the timing based on a transmission cycle regarding a held message inorder to inform the transmission cycle to an apparatus transmittinganother message. Then, the apparatus transmitting a message regardingthe message hold adjusts own transmission timing based on thetransmission timing regarding the instruction message, and utilizes theadjusted reference timing to transmit the subsequent messages regardingthe message hold. Therefore, it is possible to make each apparatus knowthe transmission timing for the message regarding the message hold.Hence, it is efficient.

According to the sixteenth aspect, it is controlled to transmit messagesother than the message regarding the message hold at transmissiontimings that are different from the transmission timing utilized for themessage regarding the message hold. Thus, the control is performed toprevent many messages from reaching to the relay apparatus after themessage regarding the message hold reaches. Therefore, it is possible toprevent the message hold from becoming longer and larger at the relayapparatus, and to improve the communication efficiency.

In the present invention, it may be configured to make each apparatusconnected to a communication line with a bus topology perform thetransmission timing adjustment, and to perform the adjustment only wheneach apparatus determines that the adjustment should be performed.Therefore, it is possible to reduce the processing load of eachcommunication apparatus, to efficiently prevent the communicationcollision, to effectively adjust the transmission timing, and to improvethe communication efficiency.

In the present invention, it may be configured to make each apparatusconnected to a communication line with a bus topology perform thetransmission timing adjustment, to determine in accordance with acounted number of messages transmitted on the communication line whetherthe present is in a condition requiring to perform the adjustment, e.g.,the condition causing the collision, and to perform the adjustment onlywhen the adjustment is required. Therefore, it is possible to reduce theprocessing load of each communication apparatus, to efficiently preventthe communication collision, to effectively adjust the transmissiontiming, and to improve the communication efficiency.

In the present invention, the transmission timing is adjusted when themessage hold occurs due to the relay apparatus. It is possible after theadjustment to prevent a message from being unnecessarily held at therelay apparatus relaying the message transmission between pluralapparatuses connected to a communication line with a but topology. Inaddition, when the relay apparatus receiving messages from respectiveapparatuses has determined that the adjustment should be performed, theinstruction message is transmitted to perform the transmission timingadjustment. Therefore, it is possible to reduce the processing load ofeach communication apparatus, to efficiently prevent the communicationcollision, to effectively adjust the transmission timing, and to improvethe communication efficiency as the entire system, in comparison withthe case that each apparatus constantly performs the transmission timingadjustment.

Especially, the on-vehicle LAN performing a wire communicating throughcommunication lines connected with a bus topology is desired to performthe efficient high speed communication, with reducing the communicationcollision, but without utilizing a resolution method making thecommunication speed become faster and giving a large amount ofprocessing load on each apparatus. Even in such an especial case, thepresent invention can effectively reduce the communication collision onthe communication line and can improve the communication efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further objects and features of the invention will morefully be apparent from the following detailed description withaccompanying drawings.

FIG. 1 is a configuration view showing a configuration of an on-vehiclecommunication system according to an embodiment 1.

FIG. 2 is a block diagram showing components included in an ECU and arelay apparatus that configure the on-vehicle communication systemaccording to the embodiment 1.

FIG. 3 is an explanation view showing an example of contents included ina message transmitted between ECUs that are connected to a communicationline according to the embodiment 1.

FIG. 4 is an explanation view showing an example of contents included ina relay table according to the embodiment 1.

FIG. 5 is an explanation view showing an example of groups classifiedfor performing a transmission timing adjustment according to theembodiment 1.

FIG. 6 is a simplified scheme for explaining a transmission timingadjustment performed by the ECU according to the embodiment 1.

FIG. 7A shows a time distribution based on time points for transmittingrespective messages before the ECU performs the transmission timingadjustment according to the embodiment 1.

FIG. 7B shows a time distribution based on time points for transmittingrespective messages after the ECU performs the transmission timingadjustment according to the embodiment 1.

FIG. 8 is a flowchart showing an example of a procedure regarding amessage observation processing and an adjustment requirementdetermination processing performed by a controlling unit included in arelay apparatus according to the embodiment 1.

FIG. 9 is a flowchart showing an example of a procedure regarding anadjustment requirement determination processing performed by adetermining unit included in the relay apparatus according to theembodiment 1.

FIG. 10 is a view for explaining an example of the determinationprocessing performed by the determining unit according to the embodiment1.

FIG. 11 is a flowchart showing an example of a procedure regarding theadjustment requirement determination processing performed by thedetermining unit included in the relay apparatus according to anembodiment 2.

FIG. 12 is a view for explaining an example of the determinationprocessing performed by the determining unit according to the embodiment2.

FIG. 13 is a flowchart showing an example of a procedure regarding theadjustment requirement determination processing performed by thedetermining unit included in the relay apparatus according to anembodiment 3.

FIG. 14 is a view for explaining an example of the determinationprocessing performed by the determining unit according to the embodiment3.

FIG. 15 is a view showing a configuration of the on-vehiclecommunication system according to an embodiment 4.

FIG. 16 is a block diagram showing components included in the ECU andthe relay apparatus that configure the on-vehicle communication systemaccording to the embodiment 4.

FIG. 17 is a flowchart showing an example of a procedure performed whenthe controlling unit included in the relay apparatus according to theembodiment 4 instructs to perform the transmission timing adjustment.

FIG. 18 is a flowchart showing an example of a procedure regarding adetermination processing performed by the determining unit included inthe relay apparatus according to the embodiment 4, whether a message isheld or not.

FIG. 19 is a flowchart showing another example of the procedureregarding the determination processing performed by the determining unitincluded in the relay apparatus according to the embodiment 4, whether amessage is held or not.

FIG. 20 is a flowchart showing an example of the procedure performedwhen the controlling unit included in the relay apparatus according toan embodiment 5 instructs to perform the transmission timing adjustment.

FIG. 21 is a flowchart showing an example of a procedure performed bythe ECU according to the embodiment 5 for adjusting the transmissiontiming based on an instruction message.

FIG. 22 is an explanation view schematically showing an example ofresults obtained from the transmission timing adjustment performed bythe ECU according to the embodiment 5.

FIG. 23A is an explanation view showing an example case that a collisionoccurs on communication of data transmitted from an ECU through acommunication line.

FIG. 23B is an explanation view showing the example case that thecollision occurs on communication of data transmitted from the ECUthrough the communication line.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in reference to figures thatshow embodiments according to the present invention. The embodimentdescribed below is explained in the context of on-vehicle communicationsystem, in which ECUs mounted on a car are connected, a relay apparatusrelays data transmitted between the ECUs, and a communication apparatusaccording to the present invention is utilized as the relay apparatus.

(Embodiment 1)

FIG. 1 is a configuration view showing a configuration of the on-vehiclecommunication system according to an embodiment 1. The on-vehiclecommunication system includes: ECUs 1, 1, . . . that are apparatusestransmitting messages; communication lines 2 a, 2 b, each of which isconnected to a group of ECUs 1, 1, . . . ; and a relay apparatus 3 thatis connected to communication lines 2 a, 2 b and relays data transmittedbetween ECUs 1, 1, . . . .

ECUs 1, 1, . . . are respectively connected to communication lines 2 a,2 b with a bus topology. For implementing functions of car, the ECUs 1,1, . . . can transmit data including numerical information representingseveral physical values, such as a counted value, calculated value andcontrol value, or can control an engine, brake and the like, with amicrocomputer. When transmitting data including the numericalinformation, the ECUs 1, 1, . . . performs transmission based on thecontroller area network (CAN) protocol of a “message” including pluralarranged data and being provided with a message ID based on the arrangedplural data.

The communication lines 2 a, 2 b are connected with the bus topology toa relay apparatus 3, too. The relay apparatus 3 can receive all messagestransmitted to the communication lines 2 a, 2 b.

The on-vehicle communication system described below is configured tomake ECUs 1, 1, . . . controlled by the relay apparatus 3 adjust amessage transmission timing in association with each other, forimproving the communication efficiency on the communication lines 2 a, 2b.

FIG. 2 is a block diagram showing components included in the ECU 1 andthe relay apparatus 3 that configure the on-vehicle communication systemaccording to the embodiment 1. The ECU 1 includes: a controlling unit 10that consists of a central processing unit (CPU), a micro processingunit (MPU) or the like, and controls processing of each component; astoring unit 11 that consists of a memory, such as anelectrically-erasable programmable read-only memory (EEPROM) or a flashmemory; a clocking unit 12 that implements a timer function; and acommunicating unit 13 that implements communication through thecommunication line 2 a (or communication line 2 b).

The controlling unit 10 of ECU 1 is configured to obtain electric powerfrom a power supply apparatus (not shown), such as a battery oralternator mounted on the car, for controlling each component. Thestoring unit 11 stores computer program for implementing transmissiontiming adjustment described later or several information utilized by thecontrolling unit 10 to perform processing.

The clocking unit 12 clocks elapsed time with a predetermined frequency.The controlling unit 10 can obtain time information from the clockingunit 12 at a predetermined timing.

The communicating unit 13 is equipped with a network controller chip ora network controller function, and implements the communication throughthe communication line 2 a (or communication line 2 b). In thecommunication between the ECUs 1, 1, . . . and the relay apparatus 3through the communication lines 2 a, 2 b, it is configured to transmit amessage based on the CAN protocol. Therefore, the communicating unit 13performs the message transmission based on the CAN protocol through thecommunication line 2 a (or communication line 2 b). For example, thecontrolling unit 10 of ECU 1 connected to the communication line 2 autilizes the communicating unit 13 to monitor communication conditionson the communication line 2 a, determines whether the controlling unit10 of ECU 1 itself can transmit a message or not, and transmits themessage when possible. Typically, the ECU 1 can make the communicatingunit 13 transmit the message, during a period that a message istransmitted neither by the other ECUs 1, 1, . . . similarly connected tothe communication line 2 a nor by the relay apparatus 3. In the CANdefinition, the message ID works as the arbitration field. In the casethat the message ID is represented in the binary number system, amessage whose message ID possesses a longer zero bit string ispreferentially transmitted. Thus, in the case that the message ID isinterpreted to be a numerical value, a message whose ID is interpretedto be a smaller number is preferentially transmitted. When pluralapparatuses has simultaneously tried to transmit messages among the ECUs1, 1, . . . and relay apparatus 3 connected to the communication line 2a, a message whose message ID is the smallest is transmitted at first.In addition, when any of the ECUs 1, 1, . . . and relay apparatus 3connected to the communication line 2 a are transmitting messagesthrough the communication line 2 a, the other ECUs 1, 1, . . . connectedto the communication line 2 a can simultaneously receive messages.

The ECUs 1, 1, . . . described above can cyclically transmit messages inaccordance with the timer function implemented by the clocking unit 12.It is configured to set the cycle for each message. Thus, in the casethat one ECU 1 transmits messages, a message may be cyclicallytransmitted every ten milliseconds and another message may be cyclicallytransmitted every twenty-five milliseconds. In addition, each of theECUs 1, 1, . . . performs timing adjustment on message transmission inassociation with another ECU 1, as described later.

The relay apparatus 3 includes: a controlling unit 30 that consists ofthe CPU, MPU or the like and controls each component; a storing unit 31that consists of a memory, such as an EEPROM or the flash memory; atemporary storing unit 32 that consists of a memory, such as a DRAM orSRAM; a clocking unit 33 that implements the timer function; a firstcommunicating unit 34 that is connected to the communication line 2 a; asecond communicating unit 35 that is connected to the communication line2 b; and a determining unit 36 that monitors communication condition onthe communication lines 2 a, 2 b and determines whether the transmissiontiming adjustment should be performed or not.

The controlling unit 30 is configured to obtain electric power from apower supply apparatus (not shown), such as a battery or alternatormounted on the car, for controlling each component.

The storing unit 31 stores a relay table 37 including message IDs thatrepresent messages to be relayed, and the controlling unit 30 can referthe relay table 37 to perform the relay processing.

The temporary storing unit 32 temporarily stores information generatedfrom the processing performed by the controlling unit 30, and ispartially utilized as a buffer to store received messages for the relayprocessing.

The clocking unit 33 clocks elapsed time with a predetermined frequency.The controlling unit 30 can obtain time information from the clockingunit 33 at a predetermined timing.

The first communicating unit 34 and the second communicating unit 35implement the message transmission with the ECUs 1, 1, . . . connectedthrough the communication lines 2 a, 2 b to these communicating units34, 35. In other words, these communicating units 34, 35 perform themessage transmission based on the CAN protocol.

The determining unit 36 determines whether the transmission timingadjustment described later is required or not, in accordance withmessages received by the first communicating unit 34 and the secondcommunicating unit 35. When having determined that the transmissiontiming adjustment is required, the determining unit 36 informs thedetermination result to the controlling unit 30.

In the on-vehicle communication system described above, the ECUs 1, 1, .. . cyclically transmit messages at the transmission cycle that ispreviously set. In the case that an ECU 1 utilizes a start time for thetransmission cycle and the start time is different from another starttime utilized by another ECU 1, a transmission timing utilized by theECU 1 is unlikely to overlap with another transmission timing utilizedby another ECU 1. However, the start time utilized by the ECU 1 may beshifted due to the processing performed by the ECU 1, the transmissioncycle utilized by the ECU 1 may be synchronized with anothertransmission cycle utilized by another ECU 1, and then, the transmissiontiming utilized by the ECU 1 may always overlap with anothertransmission timing utilized by another ECU 1. When the ECUs 1, 1, . . .connected to the same communication line 2 a (or communication line 2 b)have simultaneously tried to transmit messages, the collision may occurand the communication efficiency may be reduced. When the collision hasoccurred and there is a message whose transmission is deferred due tothe lower priority, the transmission of deferred message may be furtherdiffered due to a later generated message that has a higher priority andis transmitted earlier than the deferred message. Thus, the delay mayoccur and the communication efficiency may be reduced. When the controlis performed to prevent the transmission timing from overlapping withanother transmission timing, the transmission is performed smoothlyregardless of the degree of priority, and the communication efficiencyis improved.

Because of the reasons described above, the on-vehicle communicationsystem according to the embodiment 1 controls to make ECUs perform theadjustment in association with each other, prevents transmission timingsof ECUs from overlapping with each other, and implements the uniformtransmission having no bias, for improving the communication efficiency.

Each message is statically set to be transmitted by any of ECUs 1, 1, .. . , and to be received and utilized for the control by any of ECUs 1,1, . . . . Each of ECUs 1, 1, . . . stores message IDs assigned tomessages transmitted from itself, message IDs assigned to messagesreceived by itself, transmission cycles and the like, in own storingunit 11. Each of ECUs 1, 1, . . . generates and transmits a message atthe stored transmission cycle, in accordance with the timer functionimplemented by own clocking unit 12.

FIG. 3 is an explanation view showing an example of contents included ina message transmitted between the ECUs 1, 1, . . . that are connected tothe communication line 2 a according to the embodiment 1. The messagetransmitted between the ECUs 1, 1, . . . is assigned with a message IDbased on the contents included in the message. In the explanation viewof FIG. 3, “010”, “200” and the like are assigned as the message IDs. Inthe explanation view of FIG. 3, each message ID is represented by elevenbits. For example, “010” represents “(0)000 0001 0000” with thehexadecimal number system, and “200” represents “(0)010 0000 0000” withthe hexadecimal number system. Assume the case that the message ID isinterpreted to be a numerical value. In the assumed case, a messagehaving a smaller message ID is interpreted to have a higher priority. Inshort, the message having the message ID “010” has the highest priorityin the explanation view of FIG. 3. In the explanation view of FIG. 3,the degree of priority is represented with numbers indicating thepriority order.

Although a transmitted message may be received at the delayed time, eachmessage is previously set to have or not to have the permission of delayin accordance of contents included in each message. In the example shownby the explanation view of FIG. 3, the message having the message ID“050 [i.e., (0)000 0101 0000]” has the permission of delay, but themessage having the message ID “010” does not have the permission ofdelay.

In addition, each message is classified into a family A, family B orfamily C, in accordance with the contents included in each message. Forexample, ECUs 1, 1, . . . performing the body system control of a carare classified into a family regarding light parts, family regardingdoor parts, family regarding window parts and the like. Messagesrelating to the same family are likely utilized simultaneously.Therefore, a message relating to a family should be received by ECUs 1,1, . . . at a timing as close as possible to another timing when anothermessage relating to the same family is received by the ECUs 1, 1, . . ..

FIG. 4 is an explanation view showing an example of contents included inthe relay table 37 according to the embodiment 1. As shown in FIG. 4,the relay table 37 includes message IDs representing messages to berelayed and information representing relay sources and relaydestinations. The “relay source” is the communication line 2 a orcommunication line 2 b connected to the transmission source ECU 1 thathas transmitted the message, and the “relay destination” is thecommunication line 2 a or communication line 2 b connected to thetransmission destination ECU 1 that should receive the transmittedmessage. In the example shown by FIG. 4, “0 (zero)” represents thecommunication line 2 a, and “1” represents the communication line 2 b.When a message having a message ID “010” has been transmitted to thecommunication line 2 a and has been received by the first communicatingunit 34 included by the relay apparatus, the controlling unit 30included by the relay apparatus 3 temporarily stores the receivedmessage in a buffer of the temporary storing unit 32, determines inreference with the relay table 37 that the received message should berelayed to the communication line 2 b, and makes the secondcommunicating unit 35 transmit the received message. The controllingunit 30 included in the relay apparatus 3 determines that it is notrequired to transmit a message having a message ID which is not includedin the relay table 37.

The on-vehicle communication system according to the embodiment 1classifies the messages shown in FIG. 3 into groups based on the degreeof message priority, the presence of delay permission and the family,and makes apparatuses efficiently perform the transmission timingadjustment, in association with each other.

FIG. 5 is an explanation view showing an example of groups classifiedfor performing the transmission timing adjustment according to theembodiment 1. The messages shown by FIG. 3 are classified in the exampleshown by FIG. 5.

In the example shown by FIG. 5, messages are classified into groups (1)to (4). Messages having message IDs “010”, “020 [(0)000 0010 0000]” and“180 [(0)001 1000 0000]” are classified into the group (1), messageshaving message IDs “150 [(0)001 0101 0000]” and “200” are classifiedinto the group (2), a message having a message ID “050” is classifiedinto the group (3), and a message having a message ID “100 [(0)001 00000000]” is classified into the group (4). In FIG. 5, the “master message”means a message utilized as the standard of each group for performingthe transmission timing adjustment described later, and the number ofmaster message represents the priority order for becoming the mastermessage. If a message having the highest priority cannot be transmitteddue to, for example, a mechanical problem caused in an ECU 1 and thelike, each ECU treats a message, as the master message, having thesecond highest priority in the group including messages to betransmitted by itself.

It will be described below how the messages in FIG. 5 are classifiedinto the groups (1) to (4), respectively. At first, the messages areclassified in accordance with the presence of delay permission. In viewof the example shown by FIG. 3, messages having the message IDs “010”,“020” and “150” are classified into a group including messages whosedelays are not permitted, and messages having the message IDs “050”,“100”, “180” and “200” are classified into a group including messageswhose delays are permitted, respectively.

Then, the classified messages whose delays are not permitted are furtherclassified in accordance with the family. Thus, the messages whosedelays are not permitted are respectively classified into a group(family C) including the message with the message IDs “010” and “040”and another group (family A) including the messages with the message ID“150”.

Among the classified messages whose delays are permitted, a messagehaving the largest message ID and the lowest priority is transferredinto a group of messages which is classified in the same family butwhose delays are not permitted. In this example, a message having themessage ID “200” has the lowest priority among the classified messageswhose delays are permitted and which are classified in the family A. Amessage having the message ID “150” is also classified in the samefamily A, and thus the message having the message ID “200” istransferred into the group including the message having the message ID“150”. Then, a message having the message ID “180” has the second lowestpriority among the classified messages whose delays are permitted andwhich are classified in the family C. Messages having the message IDs“010” and “020” are also classified in the same family C, and thus themessage having the message ID “180” is transferred into the groupincluding the messages having the message IDs “010” and “020”.

Among the classified messages whose delays are permitted, the remainingmessages are respectively classified into the final groups, other thanthe messages transferred due to the lowest priority into groups ofmessage whose delays are not permitted. As the results, there are agroup including only the message having the message ID “050” and anothergroup including only the message having the message ID “100”, too.

The master message is selected for each group from the classifiedmessages whose delays are not permitted and which are classified in thesame family. At that time, it is preferred to select the message as themaster message which has the shortest transmission cycle in the samegroup, i.e., which has the highest priority in the same group (such amessage generally does not have the delay permission). Therefore, it ispossible to classify the messages into groups as shown in FIG. 5.

As the ECUs 1, . . . transmit messages in accordance with the groups ofclassified messages, the ECUs 1, 1, . . . performs the transmissiontiming adjustment in association with each other, to make thetransmission timings of messages classified into a group become close tothe transmission timing of the master message classified into the samegroup, and to make the transmission timing of the master message becomefar away from the other transmission timings of the other mastermessages.

FIG. 6 is a simplified scheme for explaining the transmission timingadjustment performed by the ECUs 1, 1, . . . according to theembodiment 1. The upper portion of FIG. 6 illustrates a relationshipbetween the transmission timing of master message and the transmissiontiming of another message classified into a group including this mastermessage. The bottom portion of FIG. 6 illustrates the magnitude of force(F) utilized for shifting the transmission timing of another messageclassified into a group including this master message closer to thetransmission timing of this master message, in accordance with the timelag between the transmission time point of said another message and thetransmission time point of this master message.

As shown in FIG. 6, ECUs 1, 1, . . . according to the embodiment 1respectively perform the transmission timing adjustment based on thereference to the transmission timing of the master message. Each of ECUs1, 1, . . . obtains the time lag (=[transmission time point of mastermessage]—[transmission time point of message transmitted by itself])that is the difference between the transmission time point of a messageclassified into a group and transmitted by itself and the transmissiontime point of the master message classified into the same group as thatof the message transmitted by the ECU 1. With the obtained time lag andthe equation (1) described below, each of ECUs 1, 1, . . . calculatesthe magnitude of force F, adds the calculated magnitude of force F tothe next transmission timing and then transmits the next message withthe changed next transmission timing. In the equation (1), the “r”represents time lag, the “G” represents a predetermined constant number,and the “g” represents a predetermined constant number.

$\begin{matrix}{\left\lbrack {{Equation}{\mspace{11mu}\;}1} \right\rbrack\mspace{616mu}} & \; \\{{F(r)} = \frac{2 \cdot G \cdot r}{\left( {r^{2} + g^{2}} \right)}} & (1)\end{matrix}$

In the case that the time point of a message transmitted by itself isearlier than the transmission time point of the master message (leftarrow in the upper portion of FIG. 6), the magnitude of force F is apositive value. Thus, the next transmission timing is delayed by aperiod corresponding to the magnitude of force F. In the contrary casethat the time point of a message transmitted by itself is later than thetransmission time point of the master message (right arrow in the upperportion of FIG. 6), the magnitude of force F is a negative value. Thus,the next transmission timing is advanced by a period corresponding tothe magnitude of force F. Although a significant larger magnitude offorce does not affect even in the case according to the embodiment 1that there is a significant large time lag between the time point of amessage transmitted by itself and the transmission time point of themaster, the time point of a message transmitted by itself is changedclosest to the transmission time point of the master in the case thatthe time lag becomes a predetermined period.

As the ECUs 1, 1, . . . described above respectively transmit themessage classified into a group including the master message, the ECUs1, 1, . . . respectively advance or delay the next transmission timingby the period corresponding to the magnitude force F calculated from thetime lag between the time point of a message transmitted by themselvesand the transmission time point of the master, in order to make the nexttransmission timing become close to the transmission timing of themaster message.

FIG. 7A and FIG. 7B are explanation views schematically showing anexample of results obtained by the transmission timing adjustmentperformed by the ECUs 1, 1, . . . according to the embodiment 1. FIG. 7Aillustrates a time distribution based on time points for transmittingrespective messages before the transmission timing adjustment isperformed, and FIG. 7B illustrates the time distribution after thetransmission timing adjustment is performed. In FIG. 7A and FIG. 7B, thehorizontal axis represents a temporal axis, and each arrow represents atransmission time point of a message. The transmission time point of amaster message is illustrated above the horizontal axis, and thetransmission time point of the other message is illustrated under thehorizontal axis.

In the example shown in FIG. 7A, the message having the message ID “010”is transmitted several times (hatched arrows). At the left side of FIG.7A, a transmission time point of the message having the message ID “180”is close to transmission time points of the messages respectively havingthe message IDs “050”, “020”, “200”, “180” and “150”. The time lagbetween the transmission time point of the message having the message ID“150” and the second transmission time point of the message having themessage ID “010” and the time lag between the transmission time point ofthe message having the message ID “100” and the third transmission timepoint of the message having the message ID “010” are relatively larger.Thus, it looks that the bias occurs in the timings of messagesrespectively transmitted from the ECUs 1, 1, . . . .

In the example shown in FIG. 7B, it contrarily looks that thetransmission timings are substantially uniformed for the master messageshaving the message IDs “050”, “010”, “150” and “100” because of thetransmission timing adjustment performed in order to make thetransmission timings become far from each other. Further, the messageshaving the message IDs “020” and “180” are respectively shifted tobecome closer to the transmission timing of the message having themessage ID “010” classified in the same group as the messages having themessage IDs “020” and “180”. In other words, the adjustment is performedto be able to receive the messages classified in the same group duringthe narrower time period. Furthermore, the transmission timing of themessage having the message ID “200” is shifted to become closer to thetransmission timing of the master message having the message ID “150”.

As described above, the transmission timings are adjusted in associationwith each other by each of ECUs 1, 1, . . . . Therefore, it is possibleto reduce the communication collision on the communication line 2 a andto improve the communication efficiency.

However, in the case that ECUs 1, 1, . . . constantly perform theprocessing described above, larger processing loads are given to theECUs 1, 1, . . . . The larger processing loads are contrary to theobject reducing the processing load of ECUs 1, 1, . . . . Especially forthe ECUs 1, 1, . . . mounted on a car, it is desired to simplify thecomponents, such as a reduction of memory. Thus, the processing shouldbe simplified, and the processing load should be reduced.

Hence, in the on-vehicle communication system according to theembodiment 1, the relay apparatus 3 determines whether the timingadjustment should be performed for the transmission between the ECUs 1,1, . . . or not and instructs to each ECU 1, 1, . . . in accordance withthe determination result, before the each ECUs 1, 1, . . . performs thetiming adjustment described above. Then, an instructed ECU 1 performsthe timing adjustment. The determination whether the timing adjustmentshould be performed is performed in accordance with the timedistribution about the number of messages transmitted on thecommunication lines 2 a, 2 b. For each base time interval, the relayapparatus 3 counts the number of messages transmitted during amonitoring period divided into plural base time intervals. The relayapparatus 3 determines that the transmission timing adjustment should beperformed, when the communication is not efficient, e.g., when the biasoccurs in the message transmission timings. Then, the relay apparatus 3instructs the ECUs 1, 1, . . . to perform the transmission timingadjustment. The relay apparatus 3 monitors all messages transmitted fromECUs 1, 1, . . . for performing the replay processing, and relays amessage to be relayed. Therefore, the processing load hardly becomessignificantly larger even in the case that the relay apparatus 3 isconfigured to observe the time distribution for all messages.

It will be described below in reference to a flowchart about the messageobservation processing and adjustment requirement determinationprocessing performed by the relay apparatus 3.

FIG. 8 is the flowchart showing an example of a procedure regarding themessage observation processing and the adjustment requirementdetermination processing performed by the controlling unit 30 includedin the relay apparatus 3 according to the embodiment 1. The controllingunit 30 utilizes the timer function implemented by the clocking unit 33to start clocking the monitoring period, and then utilizes thedetermining unit 36 to determine whether the adjustment should beperformed, while counting the message number.

Based on the timer function implemented by the clocking unit 33, thecontrolling unit 30 starts clocking a base time interval (step S1), anddetermines whether a message is transmitted to the communication line 2a (or the communication line 2 b) during the base time interval or not(step S2). At that time, a message transmitted by itself for performingthe relay processing is also included in the transmitted message fordetermination.

When having determined that a message is transmitted (step S2: YES), thecontrolling unit 30 sums the number of messages transmitted during thebase time interval (step S3), and determines whether the base timeinterval has elapsed or not (step S4). The controlling unit 30 storesthe number of messages transmitted during the base time interval summedat the step S3 into the storing unit 31. Alternatively, the controllingunit 30 may be configured to stores the summed number of messages in amemory included by the controlling unit 30.

When having determined at the step S2 that a message is not transmitted(S2: NO), the controlling unit 30 proceeds the procedure to the step S4and determines whether the base time interval has elapsed or not (S4).

When having determined that the base time interval has not elapsed yet(S4: NO), the controlling unit 30 returns the procedure to the step S2and determines whether another message is transmitted or not (S2). Whenhaving determined that the base time interval has elapsed (S4: YES), thecontrolling unit 30 determines whether the monitoring period has elapsedor not (step S5). When having determined that the monitoring period hasnot elapsed yet (S5: NO), the controlling unit 30 returns the procedureto the step S1 and starts clocking the next base time interval in orderto count the number of messages transmitted during the next base timeinterval (S1).

When having determined at the step S5 that the monitoring period haselapsed (S5: YES), the controlling unit 30 makes the determining unit 36determine in accordance with the number of messages transmitted duringthe next time interval included in the monitoring period whether thetiming adjustment should be performed for messages transmitted betweenthe ECUs 1, 1, . . . (step S6).

The controlling unit 30 determines whether the timing adjustment isdetermined at the step S6 to be performed (step S7). When havingdetermined that the timing adjustment is determined at the step S6 (S7:YES), the controlling unit 30 generates an instruction message forinstructing to perform the timing adjustment, makes the firstcommunicating unit 34 or second communicating unit 35 transmit thegenerated instruction message to the communication line 2 a orcommunication line 2 b (step S8), and then completes the procedure.

When having determined that the timing adjustment is determined at thestep S6 not to be performed (S7: NO), the controlling unit 30 determineswhether the timing adjustment is determined to be unnecessary more thanpredetermined consecutive times (step S9). When having determined thatthe timing adjustment is determined to be unnecessary less than thepredetermined consecutive times (S9: NO), the controlling unit 30 thencompletes the procedure.

When having determined that the timing adjustment is determined to beunnecessary the predetermined consecutive times or more (S9: YES), thecontrolling unit 30 generates a stop adjustment message for instructingto stop the timing adjustment performed for the ECUs 1, 1, . . . , makesthe first communicating unit 34 or second communication unit 35 transmitthe generated stop adjustment message to the communication line 2 a orcommunication line 2 b (step S10) and completes the procedure.

When the instruction message has been transmitted to the communicationline 2 a (or communication line 2 b), each of the ECUs 1, 1, . . .connected to the communication line 2 a receives the transmittedinstruction message through own communicating unit 13, starts performingthe transmission timing adjustment described above, and keeps performingthe transmission timing adjustment until receiving the stop adjustmentmessage (see FIG. 7).

FIG. 9 is a flowchart showing an example of a procedure regarding theadjustment requirement determination processing performed by thedetermining unit 36 included in the relay apparatus 3 according to theembodiment 1. The procedure described below explains in detail about thedetermination at the step S6 in the flowchart of FIG. 8 whether thetransmission timing adjustment should be performed or not.

The determining unit 36 identifies the counted number of messagestransmitted during each base time interval divided from the monitoringperiod (step S611). As the counted message number for each base timeinterval is stored in the storing unit 31 or in the memory included bythe controlling unit 30, the determining unit 36 refers the storedmessage number to perform the processing.

The determining unit 36 determines whether a number of base timeintervals during which no message is transmitted is more than apredetermined number among the base time intervals for which the countedmessage number is identified at the step S611 (step S612). When havingdetermined that the number of base time intervals is more than thepredetermined number (S612: YES), the determining unit 36 determinesthat the timing adjustment should be performed for the messagestransmitted between the ECUs 1, 1, . . . (step S613), and returns theprocedure to the step S7 shown in the flowchart of FIG. 8.

When having determined that the number of base time intervals is lessthan the predetermined number (S612: NO), the determining unit 36determines that it is not required to perform the transmission timingadjustment (step S614), and returns the procedure to the step S7 shownin the flowchart of FIG. 8.

FIG. 10 is a view for explaining an example of the determinationprocessing performed by the determining unit 36 according to theembodiment 1. In FIG. 10, the horizontal axis represents a temporalaxis, each arrow represents a time point of a message transmitted duringa base time interval included in the monitoring period, and the timedistribution is illustrated for the number of messages counted duringthe monitoring period.

The monitoring period is divided into “M” numbers of base time intervalT1, T2, . . . , TM. For example, the base time interval is the greatestcommon divisor of transmission cycles regarding transmitted messages, orthe shortest time interval among all the transmission cycles. Forexample, the monitoring period is longest time interval among all thetransmission cycles.

Message numbers counted by the controlling unit 30 are represented to be“N1”, “N2”, . . . “NM” for the base time intervals T1, T2, . . . , TM,respectively. In the example of FIG. 10, the “N2” is zero and the “N4”is also zero. In the case that the predetermined number is configured tobe “2” for the determining unit 36 determining whether the number ofbase time intervals during which no message is transmitted is more thanthe predetermined number, it is determined in the example of FIG. 10that the transmission timing adjustment should be performed (S612: YES,and S613 in FIG. 9). Then, the controlling unit 30 included by the relayapparatus 3 transmits the instruction message to instruct performing thetiming adjustment, and the timing adjustment is performed by each of theECUs 1, 1, . . . in order to alleviate the bias of transmission timings.

As described above, each of ECUs 1, 1, . . . connected to thecommunication lines 2 a, 2 b performs the transmission timing adjustmentin association with each other in the on-vehicle communication systemaccording to the embodiment 1. Therefore, it is possible to reduce thecommunication collision on the communication lines 2 a, 2 b, and toimprove the communication efficiency. In addition, the relay apparatus 3monitors messages transmitted from respective ECUs 1, 1, . . . that areconnected to the communication lines 2 a, 2 b for performing the relayprocessing, observes the communication condition on the communicationlines 2 a, 2 b, and transmits the instruction message for instructingrespective ECUs 1, 1, . . . to perform the transmission timingadjustment only when it is determined that the bias has occurred in thetimings of messages transmitted from the ECUs 1, 1, . . . . Hence, it isenough for each of ECUs 1, 1, . . . to perform the timing adjustmentafter receiving the instruction message. In other words, it is notrequired for each of ECUs 1, 1, . . . to perform the constant processingregarding the timing adjustment. Therefore, it is possible to reduce theprocessing load and to implement the efficient processing.

(Embodiment 2)

In the embodiment 1, the bias of transmission timing is considered inaccordance with the determination whether the number of base timeintervals during which no message is transmitted is more than thepredetermined number among the plural base time intervals included inthe monitoring period, and then the requirement of transmission timingadjustment for ECUs 1, 1, . . . is determined in accordance with theconsideration. In the case of an embodiment 2, however, it is consideredthat the bias occurs in the timings of messages transmitted from ECUs 1,1, . . . when the number of messages transmitted during a base timeinterval is over the limitation, and then it is, determined inaccordance with the consideration that transmission timing adjustmentshould be performed.

The hardware configuration of the on-vehicle communication systemaccording to the embodiment 2 is similar to the hardware configurationaccording to the embodiment 1, thus the same numerals are provided tothe same configuration according to the embodiment 2 which is notexplained in detail. In addition, the embodiment 2 performs thetransmission timing adjustment with ECUs 1, 1, . . . and the messagenumber observation processing with the controlling unit 30 included bythe relay apparatus 3, which are similar to those of embodiment 1 andthus not explained in detail. The following description explains indetail about the adjustment requirement determination processingperformed by the determining unit 36, which is different from theembodiment 1.

FIG. 11 is a flowchart showing an example of a procedure regarding theadjustment requirement determination processing performed by thedetermining unit 36 included in the relay apparatus 3 according to theembodiment 2. The following procedure corresponds to another example ofthe determination at the step S6 in the flowchart of FIG. 8 whether thetransmission timing adjustment should be performed or not.

The determining unit 36 identifies the message number counted for eachbase time interval divided from the monitoring period (step S621). Asthe counted message number for each base time interval is stored in thestoring unit 31 or in the memory included by the controlling unit 30,the determining unit 36 refers the stored message number to perform theprocessing.

The determining unit 36 determines whether there is a base time intervalduring which more than a predetermined number of messages aretransmitted among the base time intervals whose message numbers areidentified at the step S621 (step S622). When having determined thatthere is the base time interval during which more than the predeterminednumber of messages are transmitted (S622: YES), the determining unit 36determines that the timing adjustment of messages transmitted betweenthe ECUs 1, 1, . . . should be performed (step S623), and returns theprocedure to the step S7 in the flowchart of FIG. 8.

When having determined that there is no base time interval during whichmore than the predetermined number of messages are transmitted (S622:NO), the determining unit 36 determines that the message timingadjustment should not be performed (step S623), and returns theprocedure to the step S7 in the flowchart of FIG. 8.

In the determination processing at the step S622, it is determinedwhether there is a base time interval during which more than apredetermined number of messages are transmitted or not. The“predetermined number” herein is a number corresponding to apredetermined ratio (e.g., 80%) to the theoretical number of messagestransmittable during the base time interval which is estimated from thecommunication speed of communication lines 2 a, 2 b and size of messages(e.g., number of bytes, number of bits and the like). Thus, when thereis a base time interval during which transmittable numbers of messagesare transmitted, i.e., during which messages are transmitted with almostthe maximum frequencies, it is considered that the bias has occurred inthe transmission timings and then it is determined that the timingadjustment should be performed.

FIG. 12 is a view for explaining an example of the determinationprocessing performed by the determining unit 36 according to theembodiment 2. In FIG. 12 similarly to FIG. 10 according to theembodiment 1, the horizontal axis represents a temporal axis, each arrowrepresents a time point of a message transmitted during a base timeinterval included in the monitoring period, and the time distribution isillustrated for the number of messages counted during the monitoringperiod.

In the example of FIG. 12, the controlling unit 30 counts the messagesnumbers N1, N2, . . . , NM for the base time intervals T1, T2, . . . ,TM, respectively. It is assumed that the message number N2 for the basetime interval T2 is more than a predetermined number. In this assumedcase, the determining unit 36 determines that the transmission timingadjustment should be performed after determining whether there is a basetime interval during which the number of transmitted message is morethan a predetermined number (S622: YES and S623 in FIG. 11). Then, thecontrolling unit 30 included by the relay apparatus 3 transmits theinstruction message instructing to perform the timing adjustment, andthe timing adjustment is performed on messages transmitted between theECUs 1, 1, . . . to alleviate the bias of transmission timings.

As described above, the on-vehicle communication system according to theembodiment 2 also makes the relay apparatus 3 properly determine whetherthe transmission timing adjustment should be performed or not.Therefore, it is possible to reduce the processing load on each of ECUs1, 1, . . . caused by the performance of transmission timing adjustment,to reduce the communication collision on the communication lines 2 a, 2b and to improve the communication efficiency.

(Embodiment 3)

In the embodiment 1, the bias of transmission timing is considered inaccordance with the determination whether the number of base timeintervals during which no message is transmitted is more than thepredetermined number among the plural base time intervals included inthe monitoring period, and then the requirement of transmission timingadjustment for ECUs 1, 1, . . . is determined in accordance with theconsideration. In the case of an embodiment 3, however, it is consideredthat the bias occurs in the timings of messages transmitted from ECUs 1,1, . . . when the maximum value in the message numbers for plural basetime intervals is more than predetermined-folds of the minimum value inthe message numbers for plural base intervals, and then it is determinedin accordance with the consideration that transmission timing adjustmentshould be performed.

The hardware configuration of the on-vehicle communication systemaccording to the embodiment 3 is similar to the hardware configurationaccording to the embodiment 1, thus the same numerals are provided tothe same configuration according to the embodiment 3 which is notexplained in detail. In addition, the embodiment 3 performs thetransmission timing adjustment with ECUs 1, 1, . . . and the messagenumber observation processing with the controlling unit 30 included bythe relay apparatus 3, which are similar to those of embodiment 1 andthus not explained in detail. The following description explains indetail about the adjustment requirement determination processingperformed by the determining unit 36, which is different from theembodiment 1.

FIG. 13 is a flowchart showing an example of a procedure regarding theadjustment requirement determination processing performed by thedetermining unit 36 included in the relay apparatus 3 according to theembodiment 3. The following procedure corresponds to another example ofthe determination at the step S6 in the flowchart of FIG. 8 whether thetransmission timing adjustment should be performed or not.

The determining unit 36 identifies the message number counted for eachbase time interval divided from the monitoring period (step S631). Asthe counted message number for each base time interval is stored in thestoring unit 31 or in the memory included by the controlling unit 30,the determining unit 36 refers the stored message number to perform theprocessing.

Then, the determining unit 36 identifies the maximum value and minimumvalue in the message numbers for plural base intervals identified at thestep S631 (step S632 and step S633). Based on the maximum value andminimum value identified at the step S632 and step S633, the determiningunit 36 determines whether the maximum value is more thanpredetermined-folds of the minimum value or not (step S634). When havingdetermined that the maximum value is equal to or more thanpredetermined-folds of the minimum value (S634: YES), the determiningunit 36 determines that transmission timing adjustment should beperformed for the ECUs 1, 1, . . . (step S635) and returns the procedureto the step S7 in the flowchart of FIG. 8.

When having determined that the maximum value is less thanpredetermined-folds of the minimum value (S634: NO), the determiningunit 36 determines that the message timing adjustment is not required(step S636), and returns the procedure to the step S7 in the flowchartof FIG. 8.

FIG. 14 is a view for explaining an example of the determinationprocessing performed by the determining unit 36 according to theembodiment 3. In FIG. 14 similarly to FIG. 10 according to theembodiment 1, the horizontal axis represents a temporal axis, each arrowrepresents a time point of a message transmitted during a base timeinterval included in the monitoring period, and the time distribution isillustrated for the number of messages counted during the monitoringperiod.

In the example of FIG. 14, the controlling unit 30 counts the messagesnumbers N1, N2, . . . , NM for the base time intervals T1, T2, . . . ,TM, respectively. It is assumed that the message number N2 for the basetime interval T2 is identified as the maximum value and the messagenumber N3 for the base time interval T3 is identified as the minimumvalue. The determining unit 36 determines whether the maximum value ofmessage numbers is more than the predetermined-folds of the minimumvalue. In an example case that the “predetermined-folds” is set to be“five-folds” herein, the determining unit 36 determines that thetransmission timing adjustment should be performed (S634: YES, and S635in FIG. 13). Then, the controlling unit 30 included by the relayapparatus 3 transmits the instruction message instructing to perform thetiming adjustment, and the timing adjustment is performed on messagestransmitted between the ECUs 1, 1, . . . to alleviate the bias oftransmission timings.

As described above, the on-vehicle communication system according to theembodiment 3 also makes the relay apparatus 3 properly determine whetherthe transmission timing adjustment should be performed or not, on thebasis of the transmission timings. Therefore, it is possible to reducethe processing load on each of ECUs 1, 1, . . . caused by theperformance of transmission timing adjustment, to reduce thecommunication collision on the communication lines 2 a, 2 b and toimprove the communication efficiency.

In the embodiments 1-3, the relay apparatus 3 is configured to measurethe timings of messages transmitted by the ECUs 1, 1, . . . . However,another apparatus but not the relay apparatus 3 may measure thetransmission timings and transmit the instruction message,alternatively. Because the relay apparatus 3 is typically configured forperforming the relay processing to receive all messages transmitted fromthe ECUs connected to the communication line 2 a and to relay thereceived messages to the communication line 2 b in accordance with themessage IDs provided to the received messages, the embodiments 1-3 areconfigured to make the relay apparatus 3 measure the transmissiontimings. Even when the relay apparatus 3 is made to perform theadditional functions, such as the adjustment requirement determinationprocessing and instruction message transmission processing describedabove, the relay apparatus 3 can implement the additional functionswithout improving the performance level of relay apparatus 3 andfurther, the additional functions do not cause significantly largerprocessing loads on the relay apparatus 3. Thus, such a configuration ispreferable. In addition, because the relay apparatus 3 is connected toplural communication lines 2 a, 2 b for performing the relay processing,the single relay apparatus 3 can perform the adjustment requirementdetermination processing and instruction message transmission processingnot only on the communication line 2 a but also on the communicationline 2 b. However, the present invention is not limited to such aconfiguration. Alternatively, it may be configured to prepare anapparatus that performs the adjustment requirement determinationprocessing and instruction message transmission processing on thecommunication line 2 a, to prepare another apparatus that performs theadjustment requirement determination processing and instruction messagetransmission processing on the communication line 2 b, and torespectively connect these apparatuses to the communication lines 2 a, 2b with the bus topology. These apparatus may be prepared only forperforming the processing regarding the transmission timing adjustment,or any of ECUs 1, 1, . . . respectively connected to the communicationlines 2 a, 2 b may be utilized as these apparatuses described above forperforming the adjustment requirement determination processing andinstruction message transmission processing.

(Embodiment 4)

As the relay apparatus 3 is connected to the communication lines 2 a, 2b and relays a message between the communication lines 2 a, 2 b in anembodiment 4, the relay apparatus 3 performs the transmission timingadjustment. CAN communication performs the arbitration processing basedon the message ID for implementing the message transmission. Because thearbitration processing is performed on the communication line 2 aindependently from the communication line 2 b, a message relayed fromthe communication line 2 a may be defeated consecutively on thecommunication line 2 b against other messages having higher priorities.When further messages to be relayed are successively transmitted on thecommunication line 2 a in such a case, the relay apparatus 3 holds themessages that cannot be relayed to the communication line 2 b. Thus, theembodiment 4 described below makes a relay apparatus 4 determine whetherthe transmission timing adjustment should be performed or not andadequately perform the transmission timing adjustment, in order toprevent the message hold caused by the relay apparatus 3 from becomingmore increased.

The configuration of the on-vehicle communication system according tothe embodiment 4 is similar to the configuration according to theembodiment 1, except for the configuration regarding the relay apparatus4. Thus, the same numerals are provided to the same configurationaccording to the embodiment 4 which is not explained in detail. Theconfiguration parts different from those of the embodiment 1 will mainlybe described here.

FIG. 15 is a view showing a configuration of the on-vehiclecommunication system according to the embodiment 4. The on-vehiclecommunication system includes: the ECUs 1, 1, . . . that are apparatusestransmitting messages; the communication lines 2 a, 2 b, each of whichis connected to a group of ECUs 1, 1, . . . ; and a relay apparatus 4that is connected to the communication lines 2 a, 2 b and relays datatransmitted between the ECUs 1, 1, . . . . The relay apparatus 4 is alsoconnected to the communication lines 2 a, 2 b with the bus topology, andcan receive all messages transmitted through the communication lines 2a, 2 b.

FIG. 16 is a block diagram showing components included in the ECU 1 andthe relay apparatus 4 that configure the on-vehicle communication systemaccording to the embodiment 4. The relay apparatus 4 includes: acontrolling unit 40 that consists of the CPU, MPU or the like andcontrols each component; a storing unit 41 that consists of a memory,such as an EEPROM or the flash memory; a temporary storing unit 42 thatconsists of a memory, such as a DRAM or SRAM; a clocking unit 43 thatimplements the timer function; a first communicating unit 44 that isconnected to the communication line 2 a; a second communicating unit 45that is connected to the communication line 2 b; and a determining unit46 that monitors communication condition on the communication lines 2 a,2 b and determines whether the transmission timing adjustment should beperformed or not.

The controlling unit 40 is configured to obtain electric power from thepower supply apparatus (not shown), such as a battery or alternatormounted on the car, for controlling each component.

The storing unit 41 stores a relay table 47 including message IDs thatrepresent messages to be relayed, and the controlling unit 40 can referto the relay table 47 to perform the relay processing.

The temporary storing unit 42 temporarily stores information generatedfrom the processing performed by the controlling unit 40, and ispartially utilized as a relay buffer to temporarily store messagesreceived for the relay processing. At that time, the messages to berelayed is stored in the buffer with the first in first out (FIFO)method, read out and transmitted from the buffer.

The clocking unit 43 clocks elapsed time with a predetermined frequency.The controlling unit 40 can obtain time information from the clockingunit 43 at a predetermined timing.

The first communicating unit 44 and the second communicating unit 45implement the message transmission with the ECUs 1, 1, . . . connectedthrough the communication lines 2 a, 2 b to these communicating units44, 45. In other words, these communicating units 44, 45 perform themessage transmission based on the CAN protocol.

The determining unit 46 determines whether the buffer of temporarystoring unit 32 has stored a message that is received from one of theECUs 1, 1, . . . through the communication line 2 a or communicationline 2 b and that is not relayed yet. When having determined that thebuffer of temporary storing unit 32 has stored such a message, thedetermining unit 46 informs the determination result to the unit 40.

In the on-vehicle communication system described above, the ECUs 1, 1, .. . cyclically transmits messages at the transmission cycle that ispreviously set. In the case that an ECU 1 utilizes a start time for thetransmission cycle and the start time is different from another starttime utilized by another ECU 1, a transmission timing utilized by theECU 1 is unlikely to overlap with another transmission timing utilizedby another ECU 1. However, the start time utilized by the ECU 1 may beshifted due to the processing performed by the ECU 1, the transmissioncycle utilized by the ECU 1 may be synchronized with anothertransmission cycle utilized by another ECU 1, and then, the transmissiontiming utilized by the ECU 1 may always overlap with anothertransmission timing utilized by another ECU 1. When the ECUs 1, 1, . . .connected to the same communication line 2 a (or communication line 2 b)have simultaneously tried to transmit messages, the collision may occurand the communication efficiency may be reduced. When the collision hasoccurred and there is a message whose transmission is deferred due tothe lower priority, the transmission of deferred message may be furtherdiffered due to a later generated message that has a higher priority andis transmitted earlier than the deferred message. Thus, the delay mayoccur and the communication efficiency may be reduced.

In addition, when a message has the highest priority in messages to betransmitted from the ECUs 1, 1, . . . that are connected to thecommunication line 2 a and the message is transmitted to thecommunication line 2 a to be relayed toward the communication line 2 bfrom the ECUs 1, 1, . . . that are connected to the communication line 2abecause of the highest priority, the message may be stored in thebuffer of temporary storing unit 42 and held in the buffer without beingtransmitted to the communication line 2 b because the priority of thismessage may be lower than priorities of other messages on thecommunication line 2 b. Even when there is another message to bereceived simultaneously with the message described above by an apparatusrequiring the message described above, the apparatus cannotsimultaneously receive said another message and the message describedabove because the message described above is held by the relayapparatus.

When the control is performed to prevent the transmission timings ofother messages from overlapping with the transmission timing of the heldmessage and to transmit other messages uniformly, the transmission isperformed smoothly regardless of the degree of priority, and thecommunication efficiency is improved. Assume the case that a message isheld by the relay apparatus 4. Even when the next message reaches,without immediately, to the relay apparatus 4 a predetermined periodlater in the assumed case, the other held messages may be completelyrelayed with several trials, and it is expected to prevent the messagehold from becoming more increased and more serious.

Because of the reasons described above, the on-vehicle communicationsystem according to the embodiment 4 utilizes the relay apparatus 4 thatrelays transmitted messages, controls to make ECUs 1, 1, . . . performthe adjustment in association with each other, prevents transmissiontimings of ECUs 1, 1, . . . from overlapping with each other, andimplements the uniform transmission having no bias, for improving thecommunication efficiency on the communication lines 2 a, 2 b.

The message ID, group of classified message, contents of the relay table47 and timing adjustment processing performed by the ECUs 1, 1, . . . inthe embodiment 4 are similar to those in the embodiment 1, and thus arenot explained in detail (see FIG. 3 to FIG. 7).

The on-vehicle communication system according to the embodiment 4 makesthe relay apparatus 4 relay messages between the communication lines 2a, 2 b. Thus, even when a message defeats the other messages on thecommunication line 2 a in the arbitration and then is transmitted, themessage may be defeated by the other messages on the other communicationline 2 b in the arbitration and may be held, without being transmitted,in the temporary storing unit 42 included by the relay apparatus 4. Theheld message may be relayed with several trials, if the relay apparatus4 does not receive further messages sequentially transmitted from thecommunication line 2 a. However, when the bias occurs in thetransmission timings and the further messages are sequentiallytransmitted, the message hold at the relay apparatus 4 may become largerand more serious.

Thus, the on-vehicle communication system according to the embodiment 4makes the relay apparatus 4 determine whether a message to be relayed isheld or not, instruct each ECUs 1, 1, . . . to perform the timingadjustment for messages transmitted between the ECUs 1, 1, . . . when amessage to be relayed is held, for making the ECUs 1, 1, . . . performthe timing adjustment described above. Therefore, the timing adjustmentis performed for messages transmitted between the ECUs 1, 1, . . . whenthe relay apparatus 4 gives the instructions.

It will be described below in reference to a flowchart about the heldmessage determination processing and instruction processing for thetransmission timing adjustment performed by the relay apparatus 4, andthe processing performed by each of the ECUs 1, 1, . . . when theinstruction processing is performed for the timing adjustment.

FIG. 17 is the flowchart showing an example of a procedure performedwhen the controlling unit 40 included in the relay apparatus 4 accordingto the embodiment 4 instructs to perform the transmission timingadjustment. The controlling unit 40 repeats the procedure describedbelow with a predetermined cycle.

The controlling unit 40 makes the determining unit 46 determine whetherthe buffer of temporary storing unit 42 holds a stored message that isreceived to be relayed (step S11), and determines whether thedetermining unit 46 determines that the buffer holds such a storedmessage (step S12). The determination processing at the step S11 will bedescribed later.

When having determined at the step S12 that the buffer is not determinedto be holding such a stored message (S12: NO), the controlling unit 46ends the procedure.

When having determined at the step S12 that the buffer is determined tobe holding such a stored message (S12: YES), the controlling unit 46identifies the held message (step S13). Specifically, the controllingunit 46 identifies a message ID representing a message stored at thehead of buffer included in the temporary storing unit 42. Thecontrolling unit 46 generates an instruction message to perform thetiming adjustment for messages between the ECUs 1, 1, . . . , andtransmits the generated instruction message from the first communicatingunit 44 (or second communicating unit 45) at the side of correspondingcommunication line 2 a (or communication line 2 b) (step S14). Inaddition, the controlling unit 46 not only transmits the instructionmessage at the step S13 but also transmits information representing themessage identified at the step S13, i.e., transmits the message ID (stepS15), and completes the procedure.

The controlling unit 46 repeats the procedure described above.Therefore, the instruction message is continuously transmitted duringthe situation that the relay apparatus 4 is determined to be holding amessage, i.e., until it is determined that no message is held.

FIG. 18 is a flowchart showing an example of a procedure regarding thedetermination processing performed by the determining unit 46 includedin the relay apparatus 4 according to the embodiment 4, whether amessage is held or not. The procedure described below explains in detailabout the step S11 in the flowchart of FIG. 17.

When the controlling unit 40 has received a message, stored the receivedmessage in the buffer of temporary storing unit 42 and determined inreference to the relay table 47 stored in the storing unit 41 that thestored message should be relayed, the clocking unit 43 starts clockingthe time elapsed since the message receive time point. The determiningunit 46 can refer to the elapsed time that is clocked by the controllingunit 40. Thus, the determining unit 46 determines whether apredetermined time passes or not since the message stored in the bufferof temporary storing unit 42 is received to be relayed (step S101). Inother words, the determining unit 46 determines whether the delay timeduring the message is transmitted from the transmission source ECU 1connected to the communication line 2 a and transmitted to thecommunication line 2 b by the relay apparatus 4 is equal to or more thanthe predetermined time or not. For example, the “predetermined time” maybe calculated in reference to the permitted delay time set for eachmessage. In this example case, the determining unit 46 may utilizemessage IDs representing messages stored at the head portion of bufferto identify the permitted delay time, and may determine whether theelapsed time is over the half of permitted delay time.

When having determined at the step S101 that the elapsed time is equalto or more the predetermined time (S101: YES), i.e., when havingdetermined that the delay time is longer, the determining unit 46determines that a message is held by the relay apparatus 4 (step S102),and returns the procedure to the step S12 in the flowchart of FIG. 17.

When having determined at the step S101 that the elapsed time is lessthan the predetermined time (S101: NO), i.e., when having determinedthat the delay time is shorter, the determining unit 46 determines thata message is not held (step S103), and returns the procedure to the stepS12 in the flowchart of FIG. 17.

It should be noted that the determination performed by the determiningunit 46 whether a message is held or not is not limited to the procedureshown in the flowchart of FIG. 18. FIG. 19 is a flowchart showinganother example of the procedure regarding the determination processingperformed by the determining unit 46 included in the relay apparatus 4according to the embodiment 4, whether a message is held or not.

The determining unit 46 determines whether the number of receivedmessages stored to be relayed in the buffer of temporarily storing unit42 is not less than a predetermined value, i.e., whether the number ofmessages stored without being transmitted yet is not less than thepredetermined value (step S111).

When having determined that the number of not-yet-transmitted messagesis equal to or more than the predetermined value (S111: YES), thedetermining unit 46 determines that a message is held by the relayapparatus 4 (step S112) and returns the procedure to the step S12 in theflowchart of FIG. 17.

When having determined that the number of not-yet-transmitted messagesis less than the predetermined value (S111: NO), the determining unit 46determines that no message is held by the relay apparatus 4 (step S113)and returns the procedure to the step S12 in the flowchart of FIG. 17.

The determining unit 46 utilizes the procedure shown by the flowchart ofFIG. 18, procedure shown by the flowchart of FIG. 19 or both of theseprocedures, to determine whether a message is held or not.

When a message to be relayed is held by the relay apparatus 4, the relayapparatus 4 as described above transmits the instruction messageinstructing to perform the timing adjustment for messages transmittedbetween the ECUs 1, 1, . . . , toward the communication line 2 a (orcommunication line 2 b) connected to the transmission source ECUs 1, 1,. . . , The instruction message is transmitted to the communication line2 a (or communication line 2 b) and then each of the ECUs 1, 1, . . .connected to the communication line 2 a (or communication line 2 b)receives the transmitted instruction message through the communicatingunit 13. Thus, the ECU having received the transmitted instructionmessage basically starts performing the transmission timing adjustmentdescribed above, and continues performing the transmission timingadjustment described above until the transmission of instruction messageis stopped (see FIG. 7A and FIG. 7B).

Thus, the on-vehicle communication system according to the embodiment 4can make each of ECUs 1, 1, . . . connected to the communication lines 2a, 2 b perform the transmission timing adjustment in association witheach other, and can reduce the communication collision on thecommunication lines 2 a, 2 b. When a message is held by the relayapparatus 4, the performed transmission timing adjustment leads therelay apparatus 4 to receive messages with little bias. Therefore, it ispossible to prevent the messages held by the relay apparatus 4 frombecoming larger and more serious. As monitoring messages transmittedfrom ECUs 1, 1, . . . that are connected to the communication lines 2 a,2 b for the relay processing, the relay apparatus 4 transmits theinstruction messages to make the ECUs 1, 1, . . . perform thetransmission timing adjustment only in the condition that a message isheld. Thus, it is enough for each of ECUs 1, 1, . . . to perform thetiming adjustment only when receiving the instruction message, but it isnot required for each of ECUs 1, 1, . . . to perform the timingadjustment constantly. Therefore, it is possible to reduce theprocessing load and to implement the efficient processing.

(Embodiment 5)

The embodiment 4 is configured to make the ECUs 1, 1, . . . perform inassociation with each other the transmission timing adjustment based onthe master message when having received the instruction message in orderto prevent the transmission bias. However, an embodiment 5 leads theperformed transmission timing adjustment to prevent the overlap betweenthe transmission timing of message regarding the message hold and thetransmission timing of another message, as much as possible, when it isdetermined that a message is held by the relay apparatus 4.

The hardware configuration of the on-vehicle communication systemaccording to the embodiment 5 is similar to the hardware configurationaccording to the embodiment 4, thus the same numerals are provided tothe same configuration according to the embodiment 5 which is notexplained in detail. In addition, the embodiment 5 utilizes thedetermining unit 46 included by the relay apparatus 4 to perform theheld message determination processing, which is similar to theprocessing of embodiment 4 and thus not explained in detail. Thefollowing description explains in detail about the procedure ofinstruction message transmission processing performed by the controllingunit 40 include 1 in the relay apparatus 4 and the transmission timingadjustment processing performed by the ECUs 1, 1, . . . , which aredifferent from the embodiment 4.

FIG. 20 is a flowchart showing an example of the procedure performedwhen the controlling unit 40 included in the relay apparatus 4 accordingto the embodiment 5 instructs to perform the transmission timingadjustment. The controlling unit 40 repeats the procedure describedbelow with a predetermined cycle. In the procedure shown by theflowchart of FIG. 20, the processing similar to those of FIG. 17according to the embodiment 4 are provided with the same step numbers asthose of FIG. 17 and are not explained in detail.

The controlling unit 40 makes the determining unit 46 determine whethera message is held or not (S11), and determines whether the determiningunit 46 determines that a message is held (S12). When having determinedthat the determining unit 46 determines that a message is held (S12:YES), the controlling unit 40 identifies the held message (message IDrepresenting the held message) (S13). Next, the controlling unit 40identifies the transmission cycle regarding the held message inaccordance with the identified message ID (step S16). Then, thecontrolling unit 40 transmits an instruction message with the identifiedtransmission cycle (step S17), transmits the message ID representing theheld message (step S15) and completes the procedure.

When having determined that the determining unit 46 does not determinethat a message is held (S12: NO), the controlling unit cyclicallytransmitting the instruction message stops transmitting the instructionmessage (step S18), and ends the procedure.

As the controlling unit 40 transmits the instruction message with thetransmission cycle regarding the held message at the step S17, it ispossible to inform the transmission timing of the held message to otherECUs 1, 1, . . . , too.

As described in the embodiment 4, the ECUs 1, 1, . . . basicallyperforms the transmission timing adjustment based on the transmissiontiming of master message in response to receiving the instructionmessage. However, the ECUs 1, 1, . . . in the embodiment 5 can furtherutilize the instruction message to recognize the transmission timing ofheld message. Therefore, it is possible to perform the transmissiontiming adjustment based on the transmission timing of held message.

FIG. 21 is a flowchart showing an example of a procedure performed byeach of the ECUs 1, 1, . . . according to the embodiment 5 for adjustingthe transmission timing based on an instruction message. Each of theECUs 1, 1, . . . repeats the procedure described below.

The controlling unit 10 included by the ECU 1 determines whether thecommunicating unit 13 included by the ECU 1 receives a message or not(step S21). When having determined that the communication unit 13 doesnot receive a message (S21: NO), the controlling unit 10 returns theprocedure to the step S21.

The controlling unit 10 determines whether the received message is aninstruction message transmitted from the relay apparatus 4 or not (stepS22). When having determined that the received message is not theinstruction message (S22: NO), the controlling unit 10 ends theprocedure once and repeats the procedure from the step S21.

When having determined that the received message is the instructionmessage (S22: YES), the controlling unit 10 receives message IDinformation transmitted together with the received instruction message(step S23). In addition, the controlling unit 10 identifies thetransmission timing of instruction message, because the instructionmessage is cyclically transmitted with the transmission cycle of heldmessage during the period when it is determined that a message is held(step S24).

Next, the controlling unit 10 determines whether the message ID belongsto a message to be transmitted by the controlling unit 10 itself (stepS25). When having determined that the message ID belongs to a message tobe transmitted by the controlling unit 10 itself (S25: YES), thecontrolling unit 10 makes the communicating unit 13 transmit the messageto be transmitted with a transmission timing closer to the transmissiontiming identified at the step S24 (step S26), and completes theprocedure.

The information transmitted together with the instruction messagerepresents the message ID identifying the message held by the relayapparatus 4. Thus, when the controlling unit 10 has determined that themessage ID belongs to a message to be transmitted by the controllingunit 10 itself, the controlling unit 10 can recognize that the messageto be transmitted by the controlling unit 10 itself is held by the relayapparatus 4. As the relay apparatus 4 transmits the instruction messageutilized as the standard regarding the held message transmission timingin order to inform the ECUs 1, 1, . . . of the held message transmissiontiming, an ECU 1 obligated to transmit the held message transmits theheld message with the transmission timing adjusted to the transmissiontiming of the instruction message.

When having determined at the step S25 that the message ID does notbelong to a message to be transmitted by the controlling unit 10 itself(S25: NO), the controlling unit 10 makes the communicating unit 13transmit the message to be transmitted with a transmission timing farfrom the transmission timing of the instruction message identified atthe step S24 (step S27), and ends the procedure.

The controlling unit 10 adjusts the transmission timing at the step S27because of the reasons described below, specifically. Each of the ECUs1, 1, . . . transmits a message with the transmission cycle. After theinstruction message is transmitted, the processing at the steps S25 andS26 described above start leading the held message to be cyclicallytransmitted from the corresponding ECU 1 at the time point when theinstruction message is transmitted or at another time point close to thetime point set forth. Thus, other ECUs 1, 1, . . . transmit own messageswith own transmission timings properly different from the transmissiontiming of the held message. In other words, at the step S27, each of theother ECUs 1, 1, . . . shifts own time point starting the messagetransmission cycle based on the transmission timing utilizing the starttime point for transmitting the instruction message. For example, thecontrolling unit 10 included in each of the ECUs 1, 1, . . . utilizesthe time point starting the next transmission cycle which is the timepoint when the instruction message is transmitted plus the periodcorresponding to the half of own transmission cycle.

As described in the embodiment 4, the controlling unit 10 basicallyadjusts for each group the message transmission time point to becomecloser to the time point for transmitting the master message, andadjusts the time point for transmitting the master message to become farfrom the ether time points for transmitting the other master messages,too. However, when the message to be transmitted is classified into thegroup that includes the held message as the master message, thecontrolling unit 10 exceptionally adjusts the transmission time point tobecome far from the time point for transmitting the master message, butnot to become closer to the time point for transmitting the mastermessage. Therefore, it is possible to precisely disperse thetransmission timings, and to prevent the message hold caused by therelay apparatus 4 from becoming more increased and more serious. Forexample, even when a message is transmitted from the communication line2 a and the message is not smoothly relayed by the relay apparatus 4because the message has a priority which is relatively lower on thecommunication line 2 b, the message must be transmitted with severaltrials. When other messages are not transmitted during said severaltrials from other ECUs 1, 1, . . . connected to the communication line 2a and another message is transmitted after the relay processing isalmost completed on the message having the relatively lower priority, itis possible to efficiently perform the relay processing.

FIG. 22 is an explanation view schematically showing an example ofresults obtained from the transmission timing adjustment performed bythe ECUs 1, 1, . . . according to the embodiment 5. In FIG. 22, thehorizontal axis represents a temporal axis, and each arrow represents atransmission time point of each message. The transmission time point ofa master message is illustrated above the temporal axis, and thetransmission time point of the other message is illustrated under thetemporal axis.

In the example shown in FIG. 22, the message having the message ID “010”is transmitted several times (hatched arrows). At the left side of FIG.22, messages classified into a group (1) including the message havingthe message ID “010” as the master message are transmitted.Specifically, the message having the message ID “020” and the messagehaving the message ID “180” are transmitted. In addition, the time pointfor transmitting the message having the message ID “050” is close to thetime point for transmitting the message having the message ID “010”.

Assume that the message having the message ID “010” is determined tohave been held at the time point “t1” in FIG. 22 by the relay apparatus4. In the assumed case, the relay apparatus 4 transmits the instructionmessage together with information representing the message ID “010”identifying the held message.

The ECU 1 obligated to transmit the message having the message ID “010”performs the second transmission of message having the message ID “010”at the time point closer to the time point “t2” when the instructionmessage is received. Until it is determined that the instruction messageis not held, the message having the message ID “010” is transmitted atthe time point “t3” and the time point “t4”, in accordance with themessage transmission cycle “T”. The ECU 1 obligated to transmit themessage having the message ID “010” performs the subsequent transmissionof message having the message ID “010” at the time point closer to thetime point “t3” and at the time point closer to the time point “t4”.This ECU 1 may utilize the receive time point, as the start point, torecognize what the instruction message is transmitted with thetransmission cycle regarding the message having the message ID “010”(i.e., to identify transmission timing), and may perform the subsequenttransmission with the identified transmission timing.

When having received the instruction message, the ECUs 1, 1, . . .obligated to transmit messages having the message ID different from“010” performs the transmission at the time point far from the timepoint when the instruction message is received (or time point when theinstruction message is transmitted). Specifically, the ECU1 obligated totransmit the message having the message ID “180” adjusts thetransmission timing based on the time lag between the time point whenthe master message having the message ID “010” has been transmitted andown transmission time point. However, the adjusted transmission timingshould be far from the transmission timing regarding the instructionmessage. When the time points receiving the instruction messages aredetected several times, the start point and transmission cycle regardingthe instruction message transmission timing are identified, and theadjustment processing for becoming far from the identified timing iscontrary to the transmission timing adjustment based on the time pointfor transmitting the master message, the former adjustment processing ispreferentially performed.

Each of ECUs 1, 1, . . . may determine whether the message ID thatrepresents the held message transmitted together with the instructionmessage matches to the message ID that represents the master messageclassified into the group including own messages. When having determinedthat the message ID representing the held message matches to the messageID representing the master message, the ECU 1 may not perform thetransmission timing adjustment corresponding to the magnitude of forcebased on the time lag that is calculated from the time point fortransmitting the master message until the transmission of instructionmessages is stopped.

Thus, the transmission timing adjustment is performed to make the timelag regarding the message having the message ID “180” become larger,although the message having the message ID “010” is the master messagein the example shown in FIG. 22. For the rest, the timing is adjusted tobe farther. Furthermore, the transmission timing adjustment is performedto make the time lag regarding the message having the message ID “020”become larger after the first instruction message is received, althoughthe message having the message ID “010” is the master message.

Furthermore, the example shown in FIG. 22 illustrates the transmissiontiming adjustment performed to make the time points for transmitting themessage having the message ID “100” and message having the message ID“050” become far from the time point for transmitting the message havingthe message ID “010”.

As described above, each of the ECUs 1, 1, . . . performs thetransmission timing adjustment in association with each other.Therefore, it is possible to reduce the communication collision on thecommunication line 2 a and to improve the communication efficiency. Inaddition, the transmission cycle regarding the message held by the relayapparatus 4 is informed with the transmitted instruction message to theECUs 1, 1, . . . that ought to transmit other messages. Hence, each ofthe ECUs 1, 1, . . . can perform the transmission timing adjustment withpreventing another message from being transmitted until the held messageis completely relayed. Therefore, it is possible to prevent the heldmessage to be relayed by the relay apparatus 4 from becoming moreincreased and more serious, and to improve the communication efficiencyfor the whole on-vehicle communication system including the relayapparatus 4.

The embodiments 1 to 5 are explained in the context of on-vehiclecommunication system. However, the present invention is not limited tothe communication system mounted on a vehicle (car). The presentinvention can be applied to the communication system where data isexchanged between plural communication apparatuses, the pluralcommunication apparatuses work in association with each other, and thetransmission timing adjustment is required to prevent the collisionbetween the communication apparatuses from occurring.

It should be understood that the embodiment described herein is onlyillustrative of the present invention and that various modifications maybe made thereto without departing from the scope of the invention asdefined in the appended claims.

The invention claimed is:
 1. A vehicular communication apparatus,comprising: a connecting unit that connects to a communication lineconnected to a vehicular ECU; a determining unit that determines whethera transmission timing adjustment should be performed for a message onthe communication line or not; and an instruction transmitting unit thattransmits a performance instruction message, from the connecting unit,which instructs to perform the transmission timing adjustment when thedetermining unit has determined that the transmission timing adjustmentshould be performed.
 2. A vehicular communication apparatus according toclaim 1, wherein plural vehicular ECUs are connected to thecommunication line with a bus topology.
 3. A vehicular communicationapparatus according to claim 1, further comprising: a message numbercounting unit that counts a number of messages transmitted to thecommunication line during a monitoring period, wherein the determiningunit determines in accordance with the number counted by the messagenumber counting unit.
 4. The vehicular communication apparatus accordingto claim 3, wherein the message number counting unit cyclically countswith utilizing the monitoring period as one cycle, and when thedetermining unit has consecutively determined during a predeterminedperiod that the transmission timing adjustment should not be performed,the instruction transmitting unit transmits from the connecting unit astop instruction message that instructs to stop performing thetransmission timing adjustment.
 5. A vehicular communication apparatusaccording to claim 3, wherein the monitoring period consists of pluraltime intervals, and the message number counting unit counts a number ofmessages transmitted to the communication line during each timeinterval.
 6. A vehicular communication apparatus according to claim 5,further comprising: an obtaining unit that obtains a messagedistribution based on the number of messages counted for each timeinterval by the message number counting unit; and a setting unit thatsets a time point for starting to transmit the performance instructionmessage in accordance with the message distribution obtained by theobtaining unit, wherein when the determining unit has determined thatthe transmission timing adjustment should be performed, the instructiontransmitting unit transmits the performance instruction message at thetime point set by the setting unit.
 7. A vehicular communicationapparatus, comprising: a connecting unit that connects to acommunication line connected to a vehicular ECU; a determining unit thatdetermines whether a transmission timing adjustment should be performedfor a message on the communication line or not; an instructiontransmitting unit that transmits a performance instruction message, fromthe connecting unit, which instructs to perform the transmission timingadjustment when the determining unit has determined that thetransmission timing adjustment should be performed, a message numbercounting unit that counts a number of messages transmitted to thecommunication line during a monitoring period, wherein the determiningunit determines in accordance with the number counted by the messagenumber counting unit, wherein the monitoring period consists of pluraltime intervals, and the message number counting unit counts a number ofmessages transmitted to the communication line during each timeinterval, and wherein when not less than a predetermined number of timeintervals are indicated to have “zero” as the number counted by themessage number counting unit, the determining unit determines that thetransmission timing adjustment should be performed, and when less thanthe predetermined number of time intervals are indicated to have “zero”as the number counted by the message number counting unit, thedetermining unit does not determine that the transmission timingadjustment should be performed.
 8. A vehicular communication systemaccording to claim 7, further comprising: a hold judging unit thatjudges whether a message transmitted to the communication line is heldor not, wherein when the hold judging unit judges that the messagetransmitted to the communication line is held, the determining unitdetermines that the transmission timing adjustment should be performed,when the hold judging unit does not judge that the message transmittedto the communication line is held, the determining unit does notdetermine that the transmission timing adjustment should be performed,and said some apparatus performs the transmission timing adjustment inassociation with the other apparatuses.
 9. A vehicular communicationsystem according to claim 8, further comprising: a storing unit thatstores a message received through the communication line by the relayingunit; a message transmitting unit that cyclically transmits a messagestored in the storing unit; a timing identifying unit that identifies atiming utilized for transmitting the performance instruction message bythe instruction transmitting unit; a message identification informationtransmitting unit that transmits a message identification information tothe communication line when the performance instruction message istransmitted, the message identification information being foridentifying a message stored in the storing unit; an apparatusidentifying unit that identifies an apparatus, among the pluralapparatuses, which has transmitted the message identified with themessage identification information, wherein the instruction transmittingunit transmits the performance instruction message with a timingcorresponding to a transmission cycle utilized by the messagetransmitting unit, and the apparatus identified by the apparatusidentifying unit makes own transmission timing become closer to thetiming identified by the timing identifying unit.
 10. A vehicularcommunication system according to claim 9, wherein apparatuses otherthan the apparatus identified by the apparatus identifying unit make owntransmission timing become farther from the timing identified by thetiming identifying unit.
 11. A vehicular communication apparatus,comprising: a connecting unit that connects to a communication lineconnected to a vehicular ECU; a determining unit that determines whethera transmission timing adjustment should be performed for a message onthe communication line or not; an instruction transmitting unit thattransmits a performance instruction message, from the connecting unit,which instructs to perform the transmission timing adjustment when thedetermining unit has determined that the transmission timing adjustmentshould be performed, a message number counting unit that counts a numberof messages transmitted to the communication line during a monitoringperiod, wherein the determining unit determines in accordance with thenumber counted by the message number counting unit, wherein themonitoring period consists of plural time intervals, and the messagenumber counting unit counts a number of messages transmitted to thecommunication line during each time interval, and wherein when there isa time interval whose counted number by the message number counting unitis not less than a predetermined number, the determining unit determinesthat the transmission timing adjustment should be performed, and whenthere is no time interval whose counted number by the message numbercounting unit is not less than the predetermined number, the determiningunit does not determine that the transmission timing adjustment shouldbe performed.
 12. A communication apparatus, comprising: a connectingunit that connects to a communication line connected to a vehicular ECU;a determining unit that determines whether a transmission timingadjustment should be performed for a message on the communication lineor not; an instruction transmitting unit that transmits a performanceinstruction message, from the connecting unit, which instructs toperform the transmission timing adjustment when the determining unit hasdetermined that the transmission timing adjustment should be performed,a message number counting unit that counts a number of messagestransmitted to the communication line during a monitoring period,wherein the determining unit determines in accordance with the numbercounted by the message number counting unit, wherein the monitoringperiod consists of plural time intervals, and the message numbercounting unit counts a number of messages transmitted to thecommunication line during each time interval, and wherein when themaximum is not less than predetermined-folds of the minimum in thenumbers counted by the message number counting unit for the plural timeintervals, the determining unit determines that the transmission timingadjustment should be performed, and when the maximum is less thanpredetermined-folds of the minimum in the numbers counted by the messagenumber counting unit for the plural time intervals, the determining unitdoes not determine that the transmission timing adjustment should beperformed.
 13. A vehicular communication apparatus, comprising: aconnecting unit that connects to a communication line connected to avehicular ECU; a determining unit that determines whether a transmissiontiming adjustment should be performed for a message on the communicationline or not; an instruction transmitting unit that transmits aperformance instruction message, from the connecting unit, whichinstructs to perform the transmission liming adjustment when thedetermining unit has determined that the transmission timing adjustmentshould be performed, a message number counting unit that counts a numberof messages transmitted to the communication line during a monitoringperiod, wherein the determining unit determines in accordance with thenumber counted by the message number counting unit, a receiving unitthat receives a message through the connecting unit; and a hold judgingunit that judges whether the message received by the receiving unit isheld or not, wherein when the hold judging unit judges that the messagereceived by the receiving unit is held, the determining unit determinesthat the transmission timing adjustment should be performed, and whenthe hold judging unit does not judge that the message received by thereceiving unit is held, the determining unit does not determine that thetransmission timing adjustment should be performed, the apparatusfurther comprising: an elapsed time clocking unit that clocks a timeelapsed since the receiving unit receives a message, wherein when thetime clocked by the elapsed time clocking unit is not less than apredetermined time, the hold judging unit judges that the messagereceived by the receiving unit is held, and when the time clocked by theelapsed time clocking unit is less than the predetermined time, the holdjudging unit does not judge that the message received by the receivingunit is held.
 14. A vehicular communication apparatus according to claim13, further comprising: a storing unit that stores a message received bythe receiving unit; and an enumerating unit that enumerates a number ofmessages stored in the storing unit, wherein when the number enumeratedby the enumerating unit is not less than a predetermined number, thehold judging unit judges that the message received by the receiving unitis held, and when the number enumerated by the enumerating unit is lessthan a predetermined number, the hold judging unit does not judge thatthe message received by the receiving unit is held.
 15. A vehicularcommunication apparatus according to claim 13, further comprising: amessage transmitting unit that cyclically transmits a message stored inthe storing unit; and an identifying unit that identifies a transmissioncycle utilized by the message transmitting unit, wherein the instructiontransmitting unit utilizes a timing corresponding to the transmissioncycle identified by the identifying unit to transmit the performanceinstruction message.
 16. A vehicular communication apparatus accordingto claim 15, wherein the instruction transmitting unit continuouslytransmits the performance instruction message until the hold judgingunit judges that the message received by the receiving unit is not held.17. A vehicular communication system having a relay apparatus connectedto a communication line that is connected to plural apparatuses,comprising: a message number counting unit that counts a number ofmessages transmitted to the communication line during a monitoringperiod; a determining unit that determines in accordance with the numbercounted by the message number counting unit whether a transmissiontiming adjustment should be performed for a message on the communicationline or not; an instruction transmitting unit that transmits aperformance instruction message to the communication line whichinstructs to perform the transmission timing adjustment, when thedetermining unit determines that the transmission timing adjustmentshould be performed; a detecting unit that detects a time point when apredetermined message is transmitted, after some apparatus among theplural apparatuses receives the performance instruction message; amessage transmitting unit that cyclically transmits a message from saidsome apparatus; and a time lag sensing unit that senses a time lagbetween the time point detected by the detecting unit and a time pointwhen the message transmitting unit transmits the message, wherein themessage transmitting unit sets a next time point for transmitting a nextmessage in accordance with the time lag sensed by the time lag sensingunit.
 18. A communication method with a vehicular communicationapparatus connected to a communication line that is connected to pluralapparatuses, comprising steps of: counting a number of messagestransmitted to the communication line during a monitoring period;determining in accordance with the counted number of messages whether atransmission timing adjustment should be performed for a message on thecommunication line or not; and transmitting a performance instructionmessage from the vehicular communication apparatus when it is determinedthat the transmission timing adjustment should be performed, theperformance instruction message being for instructing to perform thetransmission timing adjustment.
 19. A communication method according toclaim 18, further comprising steps of: judging whether a messagetransmitted to the communication line is held or not; determining thatthe transmission timing adjustment should be performed, when it isjudged that the message transmitted to the communication line is held;failing to determine that the transmission timing adjustment should beperformed, when it is not judged that the message transmitted to thecommunication line is held; and controlling an apparatus having receivedthe performance instruction message to perform the transmission timingadjustment in association with the other apparatuses.